[v2] ceph: remove the extra slashes in the server path
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Message ID 20191217050231.3856-1-xiubli@redhat.com
State New
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Series
  • [v2] ceph: remove the extra slashes in the server path
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Commit Message

Xiubo Li Dec. 17, 2019, 5:02 a.m. UTC
From: Xiubo Li <xiubli@redhat.com>

When mounting if the server path has more than one slash continously,
such as:

'mount.ceph 192.168.195.165:40176:/// /mnt/cephfs/'

In the MDS server side the extra slashes of the server path will be
treated as snap dir, and then we can get the following debug logs:

<7>[  ...] ceph:  mount opening path //
<7>[  ...] ceph:  open_root_inode opening '//'
<7>[  ...] ceph:  fill_trace 0000000059b8a3bc is_dentry 0 is_target 1
<7>[  ...] ceph:  alloc_inode 00000000dc4ca00b
<7>[  ...] ceph:  get_inode created new inode 00000000dc4ca00b 1.ffffffffffffffff ino 1
<7>[  ...] ceph:  get_inode on 1=1.ffffffffffffffff got 00000000dc4ca00b

And then when creating any new file or directory under the mount
point, we can get the following crash core dump:

<4>[  ...] ------------[ cut here ]------------
<2>[  ...] kernel BUG at fs/ceph/inode.c:1347!
<4>[  ...] invalid opcode: 0000 [#1] SMP PTI
<4>[  ...] CPU: 0 PID: 7 Comm: kworker/0:1 Tainted: G            E     5.4.0-rc5+ #1
<4>[  ...] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
<4>[  ...] Workqueue: ceph-msgr ceph_con_workfn [libceph]
<4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
<4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 4d [...]
<4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
<4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
<4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
<4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
<4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
<4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
<4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
<4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
<4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
<4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
<4>[  ...] Call Trace:
<4>[  ...]  dispatch+0x2ac/0x12b0 [ceph]
<4>[  ...]  ceph_con_workfn+0xd40/0x27c0 [libceph]
<4>[  ...]  process_one_work+0x1b0/0x350
<4>[  ...]  worker_thread+0x50/0x3b0
<4>[  ...]  kthread+0xfb/0x130
<4>[  ...]  ? process_one_work+0x350/0x350
<4>[  ...]  ? kthread_park+0x90/0x90
<4>[  ...]  ret_from_fork+0x35/0x40
<4>[  ...] Modules linked in: ceph(E) libceph fscache [...]
<4>[  ...] ---[ end trace ba883d8ccf9afcb0 ]---
<4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
<4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 [...]
<4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
<4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
<4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
<4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
<4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
<4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
<4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
<4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
<4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
<4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

And we should ignore the extra slashes in the server path when mount
opening in case users have added them by mistake.

This will also help us to get an existing superblock if all the
other options are the same, such as all the following server paths
are treated as the same:

1) "//mydir1///mydir//"
2) "/mydir1/mydir"
3) "/mydir1/mydir/"

The mount_options->server_path will always save the original string
including the leading '/'.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
---
 fs/ceph/super.c | 108 +++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 93 insertions(+), 15 deletions(-)

Comments

Xiubo Li Dec. 17, 2019, 5:06 a.m. UTC | #1
Rebase to newest code with new mount API.

The following are the test cases and logs:

# ./bin/mount.ceph :////// /mnt/cephfs/

<7>[  441.397706] ceph: ceph_parse_mount_param fs_parse 'source' token 12
<7>[  441.397708] ceph:  ceph_parse_source 
'192.168.195.165:40842,192.168.195.165:40844,192.168.195.165:40846://////'
<7>[  441.397709] ceph:  device name 
'192.168.195.165:40842,192.168.195.165:40844,192.168.195.165:40846'
<7>[  441.397709] ceph:  server path '//////'
<7>[  441.397711] ceph:  ceph_get_tree
<7>[  441.399145] ceph:  set_super 000000009fcb2000
<7>[  441.399156] ceph:  get_sb using new client 00000000599fa153
<7>[  441.401617] ceph:  mount start 00000000599fa153
<6>[  441.405023] libceph: mon1 (1)192.168.195.165:40844 session established
<6>[  441.405869] libceph: client4270 fsid 
9017b7e6-dc32-472b-8ee5-00d5d799e39b
<7>[  441.405917] ceph:  mount opening path ''
<7>[  441.405932] ceph:  open_root_inode opening ''
<7>[  441.412394] ceph:  open_root_inode success
<7>[  441.412402] ceph:  open_root_inode success, root dentry is 
000000003a823af7
<7>[  441.412404] ceph:  mount success
<7>[  441.412405] ceph:  root 000000003a823af7 inode 000000003001993e 
ino 1.fffffffffffffffe
<7>[  441.412453] ceph:  destroy_mount_options 000000006a4e278a


# ./bin/mount.ceph :///mydir/// /mnt/cephfs/

<7>[  484.500470] ceph: ceph_parse_mount_param fs_parse 'source' token 12
<7>[  484.500472] ceph:  ceph_parse_source 
'192.168.195.165:40842,192.168.195.165:40844,192.168.195.165:40846:///mydir///'
<7>[  484.500473] ceph:  device name 
'192.168.195.165:40842,192.168.195.165:40844,192.168.195.165:40846'
<7>[  484.500473] ceph:  server path '///mydir///'
<7>[  484.500476] ceph:  ceph_get_tree
<7>[  484.501103] ceph:  ceph_compare_super 000000009fcb2000
<7>[  484.501105] ceph:  monitor(s)/mount options don't match
<7>[  484.501123] ceph:  ceph_compare_super 000000009fcb2000
<7>[  484.501124] ceph:  monitor(s)/mount options don't match
<7>[  484.501124] ceph:  set_super 00000000ecb2f6a5
<7>[  484.501127] ceph:  get_sb using new client 0000000050771e07
<7>[  484.501178] ceph:  mount start 0000000050771e07
<6>[  484.506726] libceph: mon0 (1)192.168.195.165:40842 session established
<6>[  484.510481] libceph: client4278 fsid 
9017b7e6-dc32-472b-8ee5-00d5d799e39b
<7>[  484.510656] ceph:  mount opening path 'mydir'
<7>[  484.510681] ceph:  open_root_inode opening 'mydir'
<7>[  484.519966] ceph:  open_root_inode success
<7>[  484.519970] ceph:  open_root_inode success, root dentry is 
0000000009d7f53d
<7>[  484.519972] ceph:  mount success
<7>[  484.519973] ceph:  root 0000000009d7f53d inode 00000000081d2db7 
ino 10000000000.fffffffffffffffe
<7>[  484.520030] ceph:  destroy_mount_options 000000006a4e278a





On 2019/12/17 13:02, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
>
> When mounting if the server path has more than one slash continously,
> such as:
>
> 'mount.ceph 192.168.195.165:40176:/// /mnt/cephfs/'
>
> In the MDS server side the extra slashes of the server path will be
> treated as snap dir, and then we can get the following debug logs:
>
> <7>[  ...] ceph:  mount opening path //
> <7>[  ...] ceph:  open_root_inode opening '//'
> <7>[  ...] ceph:  fill_trace 0000000059b8a3bc is_dentry 0 is_target 1
> <7>[  ...] ceph:  alloc_inode 00000000dc4ca00b
> <7>[  ...] ceph:  get_inode created new inode 00000000dc4ca00b 1.ffffffffffffffff ino 1
> <7>[  ...] ceph:  get_inode on 1=1.ffffffffffffffff got 00000000dc4ca00b
>
> And then when creating any new file or directory under the mount
> point, we can get the following crash core dump:
>
> <4>[  ...] ------------[ cut here ]------------
> <2>[  ...] kernel BUG at fs/ceph/inode.c:1347!
> <4>[  ...] invalid opcode: 0000 [#1] SMP PTI
> <4>[  ...] CPU: 0 PID: 7 Comm: kworker/0:1 Tainted: G            E     5.4.0-rc5+ #1
> <4>[  ...] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
> <4>[  ...] Workqueue: ceph-msgr ceph_con_workfn [libceph]
> <4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
> <4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 4d [...]
> <4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
> <4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
> <4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
> <4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
> <4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
> <4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
> <4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
> <4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
> <4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> <4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> <4>[  ...] Call Trace:
> <4>[  ...]  dispatch+0x2ac/0x12b0 [ceph]
> <4>[  ...]  ceph_con_workfn+0xd40/0x27c0 [libceph]
> <4>[  ...]  process_one_work+0x1b0/0x350
> <4>[  ...]  worker_thread+0x50/0x3b0
> <4>[  ...]  kthread+0xfb/0x130
> <4>[  ...]  ? process_one_work+0x350/0x350
> <4>[  ...]  ? kthread_park+0x90/0x90
> <4>[  ...]  ret_from_fork+0x35/0x40
> <4>[  ...] Modules linked in: ceph(E) libceph fscache [...]
> <4>[  ...] ---[ end trace ba883d8ccf9afcb0 ]---
> <4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
> <4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 [...]
> <4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
> <4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
> <4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
> <4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
> <4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
> <4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
> <4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
> <4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
> <4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> <4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
> And we should ignore the extra slashes in the server path when mount
> opening in case users have added them by mistake.
>
> This will also help us to get an existing superblock if all the
> other options are the same, such as all the following server paths
> are treated as the same:
>
> 1) "//mydir1///mydir//"
> 2) "/mydir1/mydir"
> 3) "/mydir1/mydir/"
>
> The mount_options->server_path will always save the original string
> including the leading '/'.
>
> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> ---
>   fs/ceph/super.c | 108 +++++++++++++++++++++++++++++++++++++++++-------
>   1 file changed, 93 insertions(+), 15 deletions(-)
>
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index 6f33a265ccf1..9fe1bfac66a2 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -211,7 +211,6 @@ struct ceph_parse_opts_ctx {
>   
>   /*
>    * Parse the source parameter.  Distinguish the server list from the path.
> - * Internally we do not include the leading '/' in the path.
>    *
>    * The source will look like:
>    *     <server_spec>[,<server_spec>...]:[<path>]
> @@ -232,12 +231,15 @@ static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
>   
>   	dev_name_end = strchr(dev_name, '/');
>   	if (dev_name_end) {
> -		if (strlen(dev_name_end) > 1) {
> -			kfree(fsopt->server_path);
> -			fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
> -			if (!fsopt->server_path)
> -				return -ENOMEM;
> -		}
> +		kfree(fsopt->server_path);
> +
> +		/*
> +		 * The server_path will include the whole chars from userland
> +		 * including the leading '/'.
> +		 */
> +		fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
> +		if (!fsopt->server_path)
> +			return -ENOMEM;
>   	} else {
>   		dev_name_end = dev_name + strlen(dev_name);
>   	}
> @@ -459,6 +461,64 @@ static int strcmp_null(const char *s1, const char *s2)
>   	return strcmp(s1, s2);
>   }
>   
> +/**
> + * path_remove_extra_slash - Remove the extra slashes in the server path
> + * @server_path: the server path and could be NULL
> + *
> + * Return NULL if the path is NULL or only consists of "/", or a string
> + * without any extra slashes including the leading slash(es) and the
> + * slash(es) at the end of the server path, such as:
> + * "//dir1////dir2///" --> "dir1/dir2"
> + */
> +static char *path_remove_extra_slash(const char *server_path)
> +{
> +	const char *path = server_path;
> +	bool last_is_slash;
> +	int i, j, len;
> +	char *p;
> +
> +	/* if the server path is omitted */
> +	if (!path)
> +		return NULL;
> +
> +	/* remove all the leading slashes */
> +	while (*path == '/')
> +		path++;
> +
> +	/* if the server path only consists of slashes */
> +	if (*path == '\0')
> +		return NULL;
> +
> +	len = strlen(path);
> +
> +	p = kmalloc(len, GFP_KERNEL);
> +	if (!p)
> +		return ERR_PTR(-ENOMEM);
> +
> +	last_is_slash = false;
> +	for (j = 0, i = 0; i < len; i++) {
> +		if (path[i] == '/') {
> +			if (last_is_slash)
> +				continue;
> +			last_is_slash = true;
> +		} else {
> +			last_is_slash = false;
> +		}
> +		p[j++] = path[i];
> +	}
> +
> +	/*
> +	 * remove the last slash if there has just to make sure that
> +	 * we will get "dir1/dir2"
> +	 */
> +	if (p[j - 1] == '/')
> +		j--;
> +
> +	p[j] = '\0';
> +
> +	return p;
> +}
> +
>   static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>   				 struct ceph_options *new_opt,
>   				 struct ceph_fs_client *fsc)
> @@ -466,6 +526,7 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>   	struct ceph_mount_options *fsopt1 = new_fsopt;
>   	struct ceph_mount_options *fsopt2 = fsc->mount_options;
>   	int ofs = offsetof(struct ceph_mount_options, snapdir_name);
> +	char *p1, *p2;
>   	int ret;
>   
>   	ret = memcmp(fsopt1, fsopt2, ofs);
> @@ -478,9 +539,21 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>   	ret = strcmp_null(fsopt1->mds_namespace, fsopt2->mds_namespace);
>   	if (ret)
>   		return ret;
> -	ret = strcmp_null(fsopt1->server_path, fsopt2->server_path);
> +
> +	p1 = path_remove_extra_slash(fsopt1->server_path);
> +	if (IS_ERR(p1))
> +		return PTR_ERR(p1);
> +	p2 = path_remove_extra_slash(fsopt2->server_path);
> +	if (IS_ERR(p2)) {
> +		kfree(p1);
> +		return PTR_ERR(p2);
> +	}
> +	ret = strcmp_null(p1, p2);
> +	kfree(p1);
> +	kfree(p2);
>   	if (ret)
>   		return ret;
> +
>   	ret = strcmp_null(fsopt1->fscache_uniq, fsopt2->fscache_uniq);
>   	if (ret)
>   		return ret;
> @@ -883,7 +956,7 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
>   	mutex_lock(&fsc->client->mount_mutex);
>   
>   	if (!fsc->sb->s_root) {
> -		const char *path;
> +		const char *path, *p;
>   		err = __ceph_open_session(fsc->client, started);
>   		if (err < 0)
>   			goto out;
> @@ -895,17 +968,22 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
>   				goto out;
>   		}
>   
> -		if (!fsc->mount_options->server_path) {
> -			path = "";
> -			dout("mount opening path \\t\n");
> -		} else {
> -			path = fsc->mount_options->server_path + 1;
> -			dout("mount opening path %s\n", path);
> +		p = path_remove_extra_slash(fsc->mount_options->server_path);
> +		if (IS_ERR(p)) {
> +			err = PTR_ERR(p);
> +			goto out;
>   		}
> +		/* if the server path is omitted or just consists of '/' */
> +		if (!p)
> +			path = "";
> +		else
> +			path = p;
> +		dout("mount opening path '%s'\n", path);
>   
>   		ceph_fs_debugfs_init(fsc);
>   
>   		root = open_root_dentry(fsc, path, started);
> +		kfree(p);
>   		if (IS_ERR(root)) {
>   			err = PTR_ERR(root);
>   			goto out;
Jeff Layton Dec. 17, 2019, 12:52 p.m. UTC | #2
On Tue, 2019-12-17 at 00:02 -0500, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
> 
> When mounting if the server path has more than one slash continously,
> such as:
> 
> 'mount.ceph 192.168.195.165:40176:/// /mnt/cephfs/'
> 
> In the MDS server side the extra slashes of the server path will be
> treated as snap dir, and then we can get the following debug logs:
> 
> <7>[  ...] ceph:  mount opening path //
> <7>[  ...] ceph:  open_root_inode opening '//'
> <7>[  ...] ceph:  fill_trace 0000000059b8a3bc is_dentry 0 is_target 1
> <7>[  ...] ceph:  alloc_inode 00000000dc4ca00b
> <7>[  ...] ceph:  get_inode created new inode 00000000dc4ca00b 1.ffffffffffffffff ino 1
> <7>[  ...] ceph:  get_inode on 1=1.ffffffffffffffff got 00000000dc4ca00b
> 
> And then when creating any new file or directory under the mount
> point, we can get the following crash core dump:
> 
> <4>[  ...] ------------[ cut here ]------------
> <2>[  ...] kernel BUG at fs/ceph/inode.c:1347!
> <4>[  ...] invalid opcode: 0000 [#1] SMP PTI
> <4>[  ...] CPU: 0 PID: 7 Comm: kworker/0:1 Tainted: G            E     5.4.0-rc5+ #1
> <4>[  ...] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
> <4>[  ...] Workqueue: ceph-msgr ceph_con_workfn [libceph]
> <4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
> <4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 4d [...]
> <4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
> <4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
> <4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
> <4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
> <4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
> <4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
> <4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
> <4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
> <4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> <4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> <4>[  ...] Call Trace:
> <4>[  ...]  dispatch+0x2ac/0x12b0 [ceph]
> <4>[  ...]  ceph_con_workfn+0xd40/0x27c0 [libceph]
> <4>[  ...]  process_one_work+0x1b0/0x350
> <4>[  ...]  worker_thread+0x50/0x3b0
> <4>[  ...]  kthread+0xfb/0x130
> <4>[  ...]  ? process_one_work+0x350/0x350
> <4>[  ...]  ? kthread_park+0x90/0x90
> <4>[  ...]  ret_from_fork+0x35/0x40
> <4>[  ...] Modules linked in: ceph(E) libceph fscache [...]
> <4>[  ...] ---[ end trace ba883d8ccf9afcb0 ]---
> <4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
> <4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 [...]
> <4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
> <4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
> <4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
> <4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
> <4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
> <4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
> <4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
> <4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
> <4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> <4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> And we should ignore the extra slashes in the server path when mount
> opening in case users have added them by mistake.
> 
> This will also help us to get an existing superblock if all the
> other options are the same, such as all the following server paths
> are treated as the same:
> 
> 1) "//mydir1///mydir//"
> 2) "/mydir1/mydir"
> 3) "/mydir1/mydir/"
> 
> The mount_options->server_path will always save the original string
> including the leading '/'.
> 
> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> ---
>  fs/ceph/super.c | 108 +++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 93 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index 6f33a265ccf1..9fe1bfac66a2 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -211,7 +211,6 @@ struct ceph_parse_opts_ctx {
>  
>  /*
>   * Parse the source parameter.  Distinguish the server list from the path.
> - * Internally we do not include the leading '/' in the path.
>   *
>   * The source will look like:
>   *     <server_spec>[,<server_spec>...]:[<path>]
> @@ -232,12 +231,15 @@ static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
>  
>  	dev_name_end = strchr(dev_name, '/');
>  	if (dev_name_end) {
> -		if (strlen(dev_name_end) > 1) {
> -			kfree(fsopt->server_path);
> -			fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
> -			if (!fsopt->server_path)
> -				return -ENOMEM;
> -		}
> +		kfree(fsopt->server_path);
> +
> +		/*
> +		 * The server_path will include the whole chars from userland
> +		 * including the leading '/'.
> +		 */
> +		fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
> +		if (!fsopt->server_path)
> +			return -ENOMEM;
>  	} else {
>  		dev_name_end = dev_name + strlen(dev_name);
>  	}
> @@ -459,6 +461,64 @@ static int strcmp_null(const char *s1, const char *s2)
>  	return strcmp(s1, s2);
>  }
>  
> +/**
> + * path_remove_extra_slash - Remove the extra slashes in the server path
> + * @server_path: the server path and could be NULL
> + *
> + * Return NULL if the path is NULL or only consists of "/", or a string
> + * without any extra slashes including the leading slash(es) and the
> + * slash(es) at the end of the server path, such as:
> + * "//dir1////dir2///" --> "dir1/dir2"
> + */
> +static char *path_remove_extra_slash(const char *server_path)
> +{
> +	const char *path = server_path;
> +	bool last_is_slash;
> +	int i, j, len;
> +	char *p;
> +
> +	/* if the server path is omitted */
> +	if (!path)
> +		return NULL;
> +
> +	/* remove all the leading slashes */
> +	while (*path == '/')
> +		path++;
> +
> +	/* if the server path only consists of slashes */
> +	if (*path == '\0')
> +		return NULL;
> +
> +	len = strlen(path);
> +
> +	p = kmalloc(len, GFP_KERNEL);
> +	if (!p)
> +		return ERR_PTR(-ENOMEM);
> +
> +	last_is_slash = false;
> +	for (j = 0, i = 0; i < len; i++) {
> +		if (path[i] == '/') {
> +			if (last_is_slash)
> +				continue;
> +			last_is_slash = true;
> +		} else {
> +			last_is_slash = false;
> +		}
> +		p[j++] = path[i];
> +	}
> +

Rather than walking through character by character, it might be better
to use strchr and the other string handling functions in
include/linux/string.h. Some arches have optimized string handling
routines that may perform better here.

> +	/*
> +	 * remove the last slash if there has just to make sure that
> +	 * we will get "dir1/dir2"
> +	 */
> +	if (p[j - 1] == '/')
> +		j--;
> +
> +	p[j] = '\0';
> +
> +	return p;
> +}
> +
>  static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>  				 struct ceph_options *new_opt,
>  				 struct ceph_fs_client *fsc)
> @@ -466,6 +526,7 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>  	struct ceph_mount_options *fsopt1 = new_fsopt;
>  	struct ceph_mount_options *fsopt2 = fsc->mount_options;
>  	int ofs = offsetof(struct ceph_mount_options, snapdir_name);
> +	char *p1, *p2;
>  	int ret;
>  
>  	ret = memcmp(fsopt1, fsopt2, ofs);
> @@ -478,9 +539,21 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>  	ret = strcmp_null(fsopt1->mds_namespace, fsopt2->mds_namespace);
>  	if (ret)
>  		return ret;
> -	ret = strcmp_null(fsopt1->server_path, fsopt2->server_path);
> +
> +	p1 = path_remove_extra_slash(fsopt1->server_path);
> +	if (IS_ERR(p1))
> +		return PTR_ERR(p1);
> +	p2 = path_remove_extra_slash(fsopt2->server_path);
> +	if (IS_ERR(p2)) {
> +		kfree(p1);
> +		return PTR_ERR(p2);
> +	}
> +	ret = strcmp_null(p1, p2);
> +	kfree(p1);
> +	kfree(p2);
>  	if (ret)
>  		return ret;
> +
>  	ret = strcmp_null(fsopt1->fscache_uniq, fsopt2->fscache_uniq);
>  	if (ret)
>  		return ret;
> @@ -883,7 +956,7 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
>  	mutex_lock(&fsc->client->mount_mutex);
>  
>  	if (!fsc->sb->s_root) {
> -		const char *path;
> +		const char *path, *p;
>  		err = __ceph_open_session(fsc->client, started);
>  		if (err < 0)
>  			goto out;
> @@ -895,17 +968,22 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
>  				goto out;
>  		}
>  
> -		if (!fsc->mount_options->server_path) {
> -			path = "";
> -			dout("mount opening path \\t\n");
> -		} else {
> -			path = fsc->mount_options->server_path + 1;
> -			dout("mount opening path %s\n", path);
> +		p = path_remove_extra_slash(fsc->mount_options->server_path);
> +		if (IS_ERR(p)) {
> +			err = PTR_ERR(p);
> +			goto out;
>  		}
> +		/* if the server path is omitted or just consists of '/' */
> +		if (!p)
> +			path = "";
> +		else
> +			path = p;
> +		dout("mount opening path '%s'\n", path);
>  
>  		ceph_fs_debugfs_init(fsc);
>  
>  		root = open_root_dentry(fsc, path, started);
> +		kfree(p);
>  		if (IS_ERR(root)) {
>  			err = PTR_ERR(root);
>  			goto out;
Xiubo Li Dec. 17, 2019, 2:18 p.m. UTC | #3
On 2019/12/17 20:52, Jeff Layton wrote:
> On Tue, 2019-12-17 at 00:02 -0500, xiubli@redhat.com wrote:
>> From: Xiubo Li <xiubli@redhat.com>
>>
>> When mounting if the server path has more than one slash continously,
>> such as:
>>
>> 'mount.ceph 192.168.195.165:40176:/// /mnt/cephfs/'
>>
>> In the MDS server side the extra slashes of the server path will be
>> treated as snap dir, and then we can get the following debug logs:
>>
>> <7>[  ...] ceph:  mount opening path //
>> <7>[  ...] ceph:  open_root_inode opening '//'
>> <7>[  ...] ceph:  fill_trace 0000000059b8a3bc is_dentry 0 is_target 1
>> <7>[  ...] ceph:  alloc_inode 00000000dc4ca00b
>> <7>[  ...] ceph:  get_inode created new inode 00000000dc4ca00b 1.ffffffffffffffff ino 1
>> <7>[  ...] ceph:  get_inode on 1=1.ffffffffffffffff got 00000000dc4ca00b
>>
>> And then when creating any new file or directory under the mount
>> point, we can get the following crash core dump:
>>
>> <4>[  ...] ------------[ cut here ]------------
>> <2>[  ...] kernel BUG at fs/ceph/inode.c:1347!
>> <4>[  ...] invalid opcode: 0000 [#1] SMP PTI
>> <4>[  ...] CPU: 0 PID: 7 Comm: kworker/0:1 Tainted: G            E     5.4.0-rc5+ #1
>> <4>[  ...] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
>> <4>[  ...] Workqueue: ceph-msgr ceph_con_workfn [libceph]
>> <4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
>> <4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 4d [...]
>> <4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
>> <4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
>> <4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
>> <4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
>> <4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
>> <4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
>> <4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
>> <4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> <4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
>> <4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> <4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> <4>[  ...] Call Trace:
>> <4>[  ...]  dispatch+0x2ac/0x12b0 [ceph]
>> <4>[  ...]  ceph_con_workfn+0xd40/0x27c0 [libceph]
>> <4>[  ...]  process_one_work+0x1b0/0x350
>> <4>[  ...]  worker_thread+0x50/0x3b0
>> <4>[  ...]  kthread+0xfb/0x130
>> <4>[  ...]  ? process_one_work+0x350/0x350
>> <4>[  ...]  ? kthread_park+0x90/0x90
>> <4>[  ...]  ret_from_fork+0x35/0x40
>> <4>[  ...] Modules linked in: ceph(E) libceph fscache [...]
>> <4>[  ...] ---[ end trace ba883d8ccf9afcb0 ]---
>> <4>[  ...] RIP: 0010:ceph_fill_trace+0x992/0xb30 [ceph]
>> <4>[  ...] Code: ff 0f 0b 0f 0b 0f 0b 4c 89 fa 48 c7 c6 [...]
>> <4>[  ...] RSP: 0018:ffffa23d40067c70 EFLAGS: 00010297
>> <4>[  ...] RAX: fffffffffffffffe RBX: ffff8a229eb566c0 RCX: 0000000000000006
>> <4>[  ...] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8a23aec17900
>> <4>[  ...] RBP: ffff8a226bd91eb0 R08: 0000000000000001 R09: 0000000000000885
>> <4>[  ...] R10: 000000000002dfd8 R11: ffff8a226bd95b30 R12: ffff8a239347e000
>> <4>[  ...] R13: 0000000000000000 R14: ffff8a22fabeb000 R15: ffff8a2338b0c900
>> <4>[  ...] FS:  0000000000000000(0000) GS:ffff8a23aec00000(0000) knlGS:0000000000000000
>> <4>[  ...] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> <4>[  ...] CR2: 000055b479d92068 CR3: 00000003764f6004 CR4: 00000000003606f0
>> <4>[  ...] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> <4>[  ...] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>
>> And we should ignore the extra slashes in the server path when mount
>> opening in case users have added them by mistake.
>>
>> This will also help us to get an existing superblock if all the
>> other options are the same, such as all the following server paths
>> are treated as the same:
>>
>> 1) "//mydir1///mydir//"
>> 2) "/mydir1/mydir"
>> 3) "/mydir1/mydir/"
>>
>> The mount_options->server_path will always save the original string
>> including the leading '/'.
>>
>> Signed-off-by: Xiubo Li <xiubli@redhat.com>
>> ---
>>   fs/ceph/super.c | 108 +++++++++++++++++++++++++++++++++++++++++-------
>>   1 file changed, 93 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
>> index 6f33a265ccf1..9fe1bfac66a2 100644
>> --- a/fs/ceph/super.c
>> +++ b/fs/ceph/super.c
>> @@ -211,7 +211,6 @@ struct ceph_parse_opts_ctx {
>>   
>>   /*
>>    * Parse the source parameter.  Distinguish the server list from the path.
>> - * Internally we do not include the leading '/' in the path.
>>    *
>>    * The source will look like:
>>    *     <server_spec>[,<server_spec>...]:[<path>]
>> @@ -232,12 +231,15 @@ static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
>>   
>>   	dev_name_end = strchr(dev_name, '/');
>>   	if (dev_name_end) {
>> -		if (strlen(dev_name_end) > 1) {
>> -			kfree(fsopt->server_path);
>> -			fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
>> -			if (!fsopt->server_path)
>> -				return -ENOMEM;
>> -		}
>> +		kfree(fsopt->server_path);
>> +
>> +		/*
>> +		 * The server_path will include the whole chars from userland
>> +		 * including the leading '/'.
>> +		 */
>> +		fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
>> +		if (!fsopt->server_path)
>> +			return -ENOMEM;
>>   	} else {
>>   		dev_name_end = dev_name + strlen(dev_name);
>>   	}
>> @@ -459,6 +461,64 @@ static int strcmp_null(const char *s1, const char *s2)
>>   	return strcmp(s1, s2);
>>   }
>>   
>> +/**
>> + * path_remove_extra_slash - Remove the extra slashes in the server path
>> + * @server_path: the server path and could be NULL
>> + *
>> + * Return NULL if the path is NULL or only consists of "/", or a string
>> + * without any extra slashes including the leading slash(es) and the
>> + * slash(es) at the end of the server path, such as:
>> + * "//dir1////dir2///" --> "dir1/dir2"
>> + */
>> +static char *path_remove_extra_slash(const char *server_path)
>> +{
>> +	const char *path = server_path;
>> +	bool last_is_slash;
>> +	int i, j, len;
>> +	char *p;
>> +
>> +	/* if the server path is omitted */
>> +	if (!path)
>> +		return NULL;
>> +
>> +	/* remove all the leading slashes */
>> +	while (*path == '/')
>> +		path++;
>> +
>> +	/* if the server path only consists of slashes */
>> +	if (*path == '\0')
>> +		return NULL;
>> +
>> +	len = strlen(path);
>> +
>> +	p = kmalloc(len, GFP_KERNEL);
>> +	if (!p)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	last_is_slash = false;
>> +	for (j = 0, i = 0; i < len; i++) {
>> +		if (path[i] == '/') {
>> +			if (last_is_slash)
>> +				continue;
>> +			last_is_slash = true;
>> +		} else {
>> +			last_is_slash = false;
>> +		}
>> +		p[j++] = path[i];
>> +	}
>> +
> Rather than walking through character by character, it might be better
> to use strchr and the other string handling functions in
> include/linux/string.h. Some arches have optimized string handling
> routines that may perform better here.

Will fix it, thanks.


>> +	/*
>> +	 * remove the last slash if there has just to make sure that
>> +	 * we will get "dir1/dir2"
>> +	 */
>> +	if (p[j - 1] == '/')
>> +		j--;
>> +
>> +	p[j] = '\0';
>> +
>> +	return p;
>> +}
>> +
>>   static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>>   				 struct ceph_options *new_opt,
>>   				 struct ceph_fs_client *fsc)
>> @@ -466,6 +526,7 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>>   	struct ceph_mount_options *fsopt1 = new_fsopt;
>>   	struct ceph_mount_options *fsopt2 = fsc->mount_options;
>>   	int ofs = offsetof(struct ceph_mount_options, snapdir_name);
>> +	char *p1, *p2;
>>   	int ret;
>>   
>>   	ret = memcmp(fsopt1, fsopt2, ofs);
>> @@ -478,9 +539,21 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
>>   	ret = strcmp_null(fsopt1->mds_namespace, fsopt2->mds_namespace);
>>   	if (ret)
>>   		return ret;
>> -	ret = strcmp_null(fsopt1->server_path, fsopt2->server_path);
>> +
>> +	p1 = path_remove_extra_slash(fsopt1->server_path);
>> +	if (IS_ERR(p1))
>> +		return PTR_ERR(p1);
>> +	p2 = path_remove_extra_slash(fsopt2->server_path);
>> +	if (IS_ERR(p2)) {
>> +		kfree(p1);
>> +		return PTR_ERR(p2);
>> +	}
>> +	ret = strcmp_null(p1, p2);
>> +	kfree(p1);
>> +	kfree(p2);
>>   	if (ret)
>>   		return ret;
>> +
>>   	ret = strcmp_null(fsopt1->fscache_uniq, fsopt2->fscache_uniq);
>>   	if (ret)
>>   		return ret;
>> @@ -883,7 +956,7 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
>>   	mutex_lock(&fsc->client->mount_mutex);
>>   
>>   	if (!fsc->sb->s_root) {
>> -		const char *path;
>> +		const char *path, *p;
>>   		err = __ceph_open_session(fsc->client, started);
>>   		if (err < 0)
>>   			goto out;
>> @@ -895,17 +968,22 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
>>   				goto out;
>>   		}
>>   
>> -		if (!fsc->mount_options->server_path) {
>> -			path = "";
>> -			dout("mount opening path \\t\n");
>> -		} else {
>> -			path = fsc->mount_options->server_path + 1;
>> -			dout("mount opening path %s\n", path);
>> +		p = path_remove_extra_slash(fsc->mount_options->server_path);
>> +		if (IS_ERR(p)) {
>> +			err = PTR_ERR(p);
>> +			goto out;
>>   		}
>> +		/* if the server path is omitted or just consists of '/' */
>> +		if (!p)
>> +			path = "";
>> +		else
>> +			path = p;
>> +		dout("mount opening path '%s'\n", path);
>>   
>>   		ceph_fs_debugfs_init(fsc);
>>   
>>   		root = open_root_dentry(fsc, path, started);
>> +		kfree(p);
>>   		if (IS_ERR(root)) {
>>   			err = PTR_ERR(root);
>>   			goto out;

Patch
diff mbox series

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 6f33a265ccf1..9fe1bfac66a2 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -211,7 +211,6 @@  struct ceph_parse_opts_ctx {
 
 /*
  * Parse the source parameter.  Distinguish the server list from the path.
- * Internally we do not include the leading '/' in the path.
  *
  * The source will look like:
  *     <server_spec>[,<server_spec>...]:[<path>]
@@ -232,12 +231,15 @@  static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
 
 	dev_name_end = strchr(dev_name, '/');
 	if (dev_name_end) {
-		if (strlen(dev_name_end) > 1) {
-			kfree(fsopt->server_path);
-			fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
-			if (!fsopt->server_path)
-				return -ENOMEM;
-		}
+		kfree(fsopt->server_path);
+
+		/*
+		 * The server_path will include the whole chars from userland
+		 * including the leading '/'.
+		 */
+		fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
+		if (!fsopt->server_path)
+			return -ENOMEM;
 	} else {
 		dev_name_end = dev_name + strlen(dev_name);
 	}
@@ -459,6 +461,64 @@  static int strcmp_null(const char *s1, const char *s2)
 	return strcmp(s1, s2);
 }
 
+/**
+ * path_remove_extra_slash - Remove the extra slashes in the server path
+ * @server_path: the server path and could be NULL
+ *
+ * Return NULL if the path is NULL or only consists of "/", or a string
+ * without any extra slashes including the leading slash(es) and the
+ * slash(es) at the end of the server path, such as:
+ * "//dir1////dir2///" --> "dir1/dir2"
+ */
+static char *path_remove_extra_slash(const char *server_path)
+{
+	const char *path = server_path;
+	bool last_is_slash;
+	int i, j, len;
+	char *p;
+
+	/* if the server path is omitted */
+	if (!path)
+		return NULL;
+
+	/* remove all the leading slashes */
+	while (*path == '/')
+		path++;
+
+	/* if the server path only consists of slashes */
+	if (*path == '\0')
+		return NULL;
+
+	len = strlen(path);
+
+	p = kmalloc(len, GFP_KERNEL);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	last_is_slash = false;
+	for (j = 0, i = 0; i < len; i++) {
+		if (path[i] == '/') {
+			if (last_is_slash)
+				continue;
+			last_is_slash = true;
+		} else {
+			last_is_slash = false;
+		}
+		p[j++] = path[i];
+	}
+
+	/*
+	 * remove the last slash if there has just to make sure that
+	 * we will get "dir1/dir2"
+	 */
+	if (p[j - 1] == '/')
+		j--;
+
+	p[j] = '\0';
+
+	return p;
+}
+
 static int compare_mount_options(struct ceph_mount_options *new_fsopt,
 				 struct ceph_options *new_opt,
 				 struct ceph_fs_client *fsc)
@@ -466,6 +526,7 @@  static int compare_mount_options(struct ceph_mount_options *new_fsopt,
 	struct ceph_mount_options *fsopt1 = new_fsopt;
 	struct ceph_mount_options *fsopt2 = fsc->mount_options;
 	int ofs = offsetof(struct ceph_mount_options, snapdir_name);
+	char *p1, *p2;
 	int ret;
 
 	ret = memcmp(fsopt1, fsopt2, ofs);
@@ -478,9 +539,21 @@  static int compare_mount_options(struct ceph_mount_options *new_fsopt,
 	ret = strcmp_null(fsopt1->mds_namespace, fsopt2->mds_namespace);
 	if (ret)
 		return ret;
-	ret = strcmp_null(fsopt1->server_path, fsopt2->server_path);
+
+	p1 = path_remove_extra_slash(fsopt1->server_path);
+	if (IS_ERR(p1))
+		return PTR_ERR(p1);
+	p2 = path_remove_extra_slash(fsopt2->server_path);
+	if (IS_ERR(p2)) {
+		kfree(p1);
+		return PTR_ERR(p2);
+	}
+	ret = strcmp_null(p1, p2);
+	kfree(p1);
+	kfree(p2);
 	if (ret)
 		return ret;
+
 	ret = strcmp_null(fsopt1->fscache_uniq, fsopt2->fscache_uniq);
 	if (ret)
 		return ret;
@@ -883,7 +956,7 @@  static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
 	mutex_lock(&fsc->client->mount_mutex);
 
 	if (!fsc->sb->s_root) {
-		const char *path;
+		const char *path, *p;
 		err = __ceph_open_session(fsc->client, started);
 		if (err < 0)
 			goto out;
@@ -895,17 +968,22 @@  static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
 				goto out;
 		}
 
-		if (!fsc->mount_options->server_path) {
-			path = "";
-			dout("mount opening path \\t\n");
-		} else {
-			path = fsc->mount_options->server_path + 1;
-			dout("mount opening path %s\n", path);
+		p = path_remove_extra_slash(fsc->mount_options->server_path);
+		if (IS_ERR(p)) {
+			err = PTR_ERR(p);
+			goto out;
 		}
+		/* if the server path is omitted or just consists of '/' */
+		if (!p)
+			path = "";
+		else
+			path = p;
+		dout("mount opening path '%s'\n", path);
 
 		ceph_fs_debugfs_init(fsc);
 
 		root = open_root_dentry(fsc, path, started);
+		kfree(p);
 		if (IS_ERR(root)) {
 			err = PTR_ERR(root);
 			goto out;