[4/7] proc: Use d_invalidate in proc_prune_siblings_dcache
diff mbox series

Message ID 87blpt9e6m.fsf_-_@x220.int.ebiederm.org
State New
Headers show
Series
  • proc: Dentry flushing without proc_mnt
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Commit Message

Eric W. Biederman Feb. 20, 2020, 8:49 p.m. UTC
The function d_prune_aliases has the problem that it will only prune
aliases thare are completely unused.  It will not remove aliases for
the dcache or even think of removing mounts from the dcache.  For that
behavior d_invalidate is needed.

To use d_invalidate replace d_prune_aliases with d_find_alias
followed by d_invalidate and dput.  This is safe and complete
because no inode in proc has any hardlinks or aliases.

To make this behavior change clear rename
proc_prune_siblings_dache proc_invalidate_siblings_dcache,
and rename proc_sys_prune_dcache proc_sys_invalidate_dcache.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/proc/inode.c       | 9 +++++++--
 fs/proc/internal.h    | 2 +-
 fs/proc/proc_sysctl.c | 8 ++++----
 3 files changed, 12 insertions(+), 7 deletions(-)

Comments

Linus Torvalds Feb. 20, 2020, 10:43 p.m. UTC | #1
On Thu, Feb 20, 2020 at 12:51 PM Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> To use d_invalidate replace d_prune_aliases with d_find_alias
> followed by d_invalidate and dput.  This is safe and complete
> because no inode in proc has any hardlinks or aliases.

Are you sure you can't create them some way?  This makes em go "what
if we had multiple dentries associated with that inode?" Then the code
would just invalidate the first one.

I guess we don't have export_operations or anything like that, but
this makes me worry...

            Linus
Al Viro Feb. 20, 2020, 10:54 p.m. UTC | #2
On Thu, Feb 20, 2020 at 02:49:53PM -0600, Eric W. Biederman wrote:
> 
> The function d_prune_aliases has the problem that it will only prune
> aliases thare are completely unused.  It will not remove aliases for
> the dcache or even think of removing mounts from the dcache.  For that
> behavior d_invalidate is needed.
> 
> To use d_invalidate replace d_prune_aliases with d_find_alias
> followed by d_invalidate and dput.  This is safe and complete
> because no inode in proc has any hardlinks or aliases.

s/no inode.*/it's a fucking directory inode./
Linus Torvalds Feb. 20, 2020, 11 p.m. UTC | #3
On Thu, Feb 20, 2020 at 2:54 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> s/no inode.*/it's a directory inode./

That actually makes my worry go away too. We don't allow aliases for
directory inodes, iirc.

So then it doesn't depend on some /proc implementation issue any more,
then it's fundamental that there's only one dentry.

            Linus
Al Viro Feb. 20, 2020, 11:03 p.m. UTC | #4
On Thu, Feb 20, 2020 at 10:54:20PM +0000, Al Viro wrote:
> On Thu, Feb 20, 2020 at 02:49:53PM -0600, Eric W. Biederman wrote:
> > 
> > The function d_prune_aliases has the problem that it will only prune
> > aliases thare are completely unused.  It will not remove aliases for
> > the dcache or even think of removing mounts from the dcache.  For that
> > behavior d_invalidate is needed.
> > 
> > To use d_invalidate replace d_prune_aliases with d_find_alias
> > followed by d_invalidate and dput.  This is safe and complete
> > because no inode in proc has any hardlinks or aliases.
> 
> s/no inode.*/it's a fucking directory inode./

Wait... You are using it for sysctls as well?  Ho-hum...  The thing is,
for sysctls you are likely to run into consequent entries with the
same superblock, making for a big pile of useless playing with
->s_active...  And yes, that applied to mainline as well
Eric W. Biederman Feb. 20, 2020, 11:39 p.m. UTC | #5
Al Viro <viro@zeniv.linux.org.uk> writes:

> On Thu, Feb 20, 2020 at 10:54:20PM +0000, Al Viro wrote:
>> On Thu, Feb 20, 2020 at 02:49:53PM -0600, Eric W. Biederman wrote:
>> > 
>> > The function d_prune_aliases has the problem that it will only prune
>> > aliases thare are completely unused.  It will not remove aliases for
>> > the dcache or even think of removing mounts from the dcache.  For that
>> > behavior d_invalidate is needed.
>> > 
>> > To use d_invalidate replace d_prune_aliases with d_find_alias
>> > followed by d_invalidate and dput.  This is safe and complete
>> > because no inode in proc has any hardlinks or aliases.
>> 
>> s/no inode.*/it's a fucking directory inode./
>
> Wait... You are using it for sysctls as well?  Ho-hum...  The thing is,
> for sysctls you are likely to run into consequent entries with the
> same superblock, making for a big pile of useless playing with
> ->s_active...  And yes, that applied to mainline as well

Which is why I worked to merge the two cases since they were so close.
Fewer things to fix and more eyeballs on the code.

Eric

Patch
diff mbox series

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 38a7baa41aba..c4528c419876 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -103,12 +103,13 @@  void __init proc_init_kmemcache(void)
 	BUILD_BUG_ON(sizeof(struct proc_dir_entry) >= SIZEOF_PDE);
 }
 
-void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
+void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 {
 	struct inode *inode;
 	struct proc_inode *ei;
 	struct hlist_node *node;
 	struct super_block *sb;
+	struct dentry *dentry;
 
 	for (;;) {
 		rcu_read_lock();
@@ -135,7 +136,11 @@  void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 			continue;
 		}
 
-		d_prune_aliases(inode);
+		dentry = d_find_alias(inode);
+		if (dentry) {
+			d_invalidate(dentry);
+			dput(dentry);
+		}
 		iput(inode);
 		deactivate_super(sb);
 	}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index ba9a991824a5..fd470172675f 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -210,7 +210,7 @@  extern const struct inode_operations proc_pid_link_inode_operations;
 extern const struct super_operations proc_sops;
 
 void proc_init_kmemcache(void);
-void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock);
+void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock);
 void set_proc_pid_nlink(void);
 extern struct inode *proc_get_inode(struct super_block *, struct proc_dir_entry *);
 extern void proc_entry_rundown(struct proc_dir_entry *);
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 5da9d7f7ae34..b6f5d459b087 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -267,9 +267,9 @@  static void unuse_table(struct ctl_table_header *p)
 			complete(p->unregistering);
 }
 
-static void proc_sys_prune_dcache(struct ctl_table_header *head)
+static void proc_sys_invalidate_dcache(struct ctl_table_header *head)
 {
-	proc_prune_siblings_dcache(&head->inodes, &sysctl_lock);
+	proc_invalidate_siblings_dcache(&head->inodes, &sysctl_lock);
 }
 
 /* called under sysctl_lock, will reacquire if has to wait */
@@ -291,10 +291,10 @@  static void start_unregistering(struct ctl_table_header *p)
 		spin_unlock(&sysctl_lock);
 	}
 	/*
-	 * Prune dentries for unregistered sysctls: namespaced sysctls
+	 * Invalidate dentries for unregistered sysctls: namespaced sysctls
 	 * can have duplicate names and contaminate dcache very badly.
 	 */
-	proc_sys_prune_dcache(p);
+	proc_sys_invalidate_dcache(p);
 	/*
 	 * do not remove from the list until nobody holds it; walking the
 	 * list in do_sysctl() relies on that.