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Tue, 24 Sep 2024 05:17:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id YNVNE2ZL8maFQgAAD6G6ig (envelope-from ) for ; Tue, 24 Sep 2024 05:17:26 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Subject: [PATCH 1/2] btrfs: avoid unnecessary device path update for the same device Date: Tue, 24 Sep 2024 14:47:06 +0930 Message-ID: X-Mailer: git-send-email 2.46.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Rspamd-Queue-Id: 479721F76B X-Spam-Score: -3.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.com:s=susede1]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_ONE(0.00)[1]; PREVIOUSLY_DELIVERED(0.00)[linux-btrfs@vger.kernel.org]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:dkim,suse.com:mid,suse.com:email]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_DN_NONE(0.00)[]; DWL_DNSWL_BLOCKED(0.00)[suse.com:dkim]; MIME_TRACE(0.00)[0:+]; DKIM_TRACE(0.00)[suse.com:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: [PROBLEM] It is very common for udev to trigger device scan, and every time a mounted btrfs device got re-scan from different soft links, we will get unnecessary renames like this: BTRFS: device fsid 2378be81-fe12-46d2-a9e8-68cf08dd98d5 devid 1 transid 7 /proc/self/fd/3 (253:2) scanned by mount_by_fd (11096) BTRFS info (device dm-2): first mount of filesystem 2378be81-fe12-46d2-a9e8-68cf08dd98d5 BTRFS info (device dm-2): using crc32c (crc32c-intel) checksum algorithm BTRFS info (device dm-2): using free-space-tree BTRFS info: devid 1 device path /proc/self/fd/3 changed to /dev/dm-2 scanned by (udev-worker) (11092) BTRFS info: devid 1 device path /dev/dm-2 changed to /dev/mapper/test-scratch1 scanned by (udev-worker) (11092) The program "mount_by_fd" has the following simple source code: #include #include #include int main(int argc, char *argv[]) { int fd = open(argv[1], O_RDWR); char path[256]; snprintf(path, sizeof(path), "/proc/self/fd/%d", fd); return mount(path, argv[2], "btrfs", 0, NULL); } Note that, all the above paths are all just pointing to "/dev/dm-2". The "/proc/self/fd/3" is the proc fs, describing all the opened fds. The "/dev/mapper/test-scratch1" is the soft link created by LVM2. [CAUSE] Inside device_list_add(), we are using a very primitive way checking if the device has changed, strcmp(). Which can never handle links well, no matter if it's hard or soft links. So every different link of the same device will be treated as different device, causing the unnecessary device name update. [FIX] Introduce a helper, is_same_device(), and use path_equal() to properly detect the same block device. So that the different soft links won't trigger the rename race. Signed-off-by: Qu Wenruo Reviewed-by: Filipe Manana --- fs/btrfs/volumes.c | 28 +++++++++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 995b0647f538..b713e4ebb362 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -732,6 +732,32 @@ const u8 *btrfs_sb_fsid_ptr(const struct btrfs_super_block *sb) return has_metadata_uuid ? sb->metadata_uuid : sb->fsid; } +static bool is_same_device(struct btrfs_device *device, const char *new_path) +{ + struct path old = { .mnt = NULL, .dentry = NULL }; + struct path new = { .mnt = NULL, .dentry = NULL }; + char *old_path; + bool is_same = false; + int ret; + + if (!device->name) + goto out; + + old_path = rcu_str_deref(device->name); + ret = kern_path(old_path, LOOKUP_FOLLOW, &old); + if (ret) + goto out; + ret = kern_path(new_path, LOOKUP_FOLLOW, &new); + if (ret) + goto out; + if (path_equal(&old, &new)) + is_same = true; +out: + path_put(&old); + path_put(&new); + return is_same; +} + /* * Add new device to list of registered devices * @@ -852,7 +878,7 @@ static noinline struct btrfs_device *device_list_add(const char *path, MAJOR(path_devt), MINOR(path_devt), current->comm, task_pid_nr(current)); - } else if (!device->name || strcmp(device->name->str, path)) { + } else if (!device->name || !is_same_device(device, path)) { /* * When FS is already mounted. * 1. 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Tue, 24 Sep 2024 05:17:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id GKhTHmdL8maFQgAAD6G6ig (envelope-from ); Tue, 24 Sep 2024 05:17:27 +0000 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: Fabian Vogt Subject: [PATCH 2/2] btrfs: canonicalize the device path before adding it Date: Tue, 24 Sep 2024 14:47:07 +0930 Message-ID: X-Mailer: git-send-email 2.46.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Rspamd-Queue-Id: AC98A1FBBF X-Spam-Level: X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.com:s=susede1]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_BLOCKED(0.00)[rspamd.com]; DWL_DNSWL_BLOCKED(0.00)[suse.com:dkim]; RCPT_COUNT_TWO(0.00)[2]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:url,suse.com:email,suse.com:dkim,suse.com:mid]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.com:+] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -3.01 X-Spam-Flag: NO [PROBLEM] Currently btrfs accepts any file path for its device, resulting some weird situation: # ./mount_by_fd /dev/test/scratch1 /mnt/btrfs/ The program has the following source code: #include #include #include int main(int argc, char *argv[]) { int fd = open(argv[1], O_RDWR); char path[256]; snprintf(path, sizeof(path), "/proc/self/fd/%d", fd); return mount(path, argv[2], "btrfs", 0, NULL); } Then we can have the following weird device path: BTRFS: device fsid 2378be81-fe12-46d2-a9e8-68cf08dd98d5 devid 1 transid 7 /proc/self/fd/3 (253:2) scanned by mount_by_fd (18440) Normally it's not a big deal, and later udev can trigger a device path rename. But if udev didn't trigger, the device path "/proc/self/fd/3" will show up in mtab. [CAUSE] For filename "/proc/self/fd/3", it means the opened file descriptor 3. In above case, it's exactly the device we want to open, aka points to "/dev/test/scratch1" which is another softlink pointing to "/dev/dm-2". Inside btrfs we solve the path using LOOKUP_FOLLOW, which follows the symbolic link and grab the proper block device. But we also save the filename into btrfs_device::name, still resulting the weird path. [FIX] Instead of unconditionally trust the path, check if the original file (not following the symbolic link) is inside "/dev/", if not, then manually lookup the path to its final destination, and use that as our device path. This allows us to still use symbolic links, like "/dev/mapper/test-scratch" from LVM2, which is required for fstests runs with LVM2 setup. And for really weird names, like the above case, we solve it to "/dev/dm-2" instead. Link: https://bugzilla.suse.com/show_bug.cgi?id=1230641 Reported-by: Fabian Vogt Signed-off-by: Qu Wenruo --- fs/btrfs/volumes.c | 79 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 78 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index b713e4ebb362..8acb3c465783 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -732,6 +732,70 @@ const u8 *btrfs_sb_fsid_ptr(const struct btrfs_super_block *sb) return has_metadata_uuid ? sb->metadata_uuid : sb->fsid; } +/* + * We can have very wide soft links passed in. + * One example is "/proc//fd/", which can be a soft link to + * a proper block device. + * + * But it's never a good idea to use those weird names. + * Here we check if the path (not following symlinks) is a good one inside + * "/dev/". + */ +static bool is_good_dev_path(const char *dev_path) +{ + struct path path = { .mnt = NULL, .dentry = NULL }; + char *path_buf = NULL; + char *resolved_path; + bool is_good = false; + int ret; + + path_buf = kmalloc(PATH_MAX, GFP_KERNEL); + if (!path_buf) + goto out; + + /* + * Do not follow soft link, just check if the original path is inside + * "/dev/". + */ + ret = kern_path(dev_path, 0, &path); + if (ret) + goto out; + resolved_path = d_path(&path, path_buf, PATH_MAX); + if (strncmp(resolved_path, "/dev/", strlen("/dev/"))) + goto out; + is_good = true; +out: + kfree(path_buf); + path_put(&path); + return is_good; +} + +static int get_canonical_dev_path(const char *dev_path, char *canonical) +{ + struct path path = { .mnt = NULL, .dentry = NULL }; + char *path_buf = NULL; + char *resolved_path; + int ret; + + path_buf = kmalloc(PATH_MAX, GFP_KERNEL); + if (!path_buf) { + ret = -ENOMEM; + goto out; + } + + ret = kern_path(dev_path, LOOKUP_FOLLOW, &path); + if (ret) { + pr_info("path lookup failed for %s: %d\n", dev_path, ret); + goto out; + } + resolved_path = d_path(&path, path_buf, PATH_MAX); + strncpy(canonical, resolved_path, PATH_MAX - 1); +out: + kfree(path_buf); + path_put(&path); + return ret; +} + static bool is_same_device(struct btrfs_device *device, const char *new_path) { struct path old = { .mnt = NULL, .dentry = NULL }; @@ -1408,12 +1472,23 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags, bool new_device_added = false; struct btrfs_device *device = NULL; struct file *bdev_file; + char *canonical_path = NULL; u64 bytenr; dev_t devt; int ret; lockdep_assert_held(&uuid_mutex); + if (!is_good_dev_path(path)) { + canonical_path = kmalloc(PATH_MAX, GFP_KERNEL); + if (canonical_path) { + ret = get_canonical_dev_path(path, canonical_path); + if (ret < 0) { + kfree(canonical_path); + canonical_path = NULL; + } + } + } /* * Avoid an exclusive open here, as the systemd-udev may initiate the * device scan which may race with the user's mount or mkfs command, @@ -1458,7 +1533,8 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags, goto free_disk_super; } - device = device_list_add(path, disk_super, &new_device_added); + device = device_list_add(canonical_path ? canonical_path : path, + disk_super, &new_device_added); if (!IS_ERR(device) && new_device_added) btrfs_free_stale_devices(device->devt, device); @@ -1467,6 +1543,7 @@ struct btrfs_device *btrfs_scan_one_device(const char *path, blk_mode_t flags, error_bdev_put: fput(bdev_file); + kfree(canonical_path); return device; }