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SubjectRe: [PATCH] autofs4 doesn't expire
On Tue, Aug 05, 2003 at 09:34:14PM -0700, Jeremy Fitzhardinge wrote:
> On Tue, 2003-08-05 at 21:28, Maneesh Soni wrote:
> > Sorry, I don't think it is correct. This code is called under dcache_lock,
> > taken in is_tree_busy(). mntput() calls dput() and which can lead to deadlock.
>
> Urk. On the other hand, it only calls dput if the refcount drops to
> zero, which it can't because there's already a reference (hence the -2
> in is_vfsmnt_tree_busy).
>
> I'm not too keen on releasing dcache lock, since the whole point is to
> keep the dcache tree stable while we traverse it.

yeah.. that is the problem in release dcache_lock there. How about just
doing atomic_dec(&vfs->mnt_count) in place of mntput()? This is also ugly,
but otherwise we have to re-write the entire is_tree_busy() thing.

>
> > @@ -71,7 +74,8 @@ static int check_vfsmnt(struct vfsmount
> > struct vfsmount *vfs = lookup_mnt(mnt, dentry);
> >
> > if (vfs && is_vfsmnt_tree_busy(vfs))
> > - ret--;
> > + ret = 0;
>
> Erm, why?
>

oh.. it should be ret--. I just copied Andrew's code. Following is the
corrected patch


fs/autofs4/expire.c | 15 ++++++++++++---
1 files changed, 12 insertions(+), 3 deletions(-)

diff -puN fs/autofs4/expire.c~autofs4-vfsmount-fix fs/autofs4/expire.c
--- linux-2.6.0-test2/fs/autofs4/expire.c~autofs4-vfsmount-fix 2003-08-06 09:10:49.000000000 +0530
+++ linux-2.6.0-test2-maneesh/fs/autofs4/expire.c 2003-08-06 10:25:58.000000000 +0530
@@ -25,7 +25,10 @@ static inline int is_vfsmnt_tree_busy(st
struct list_head *next;
int count;

- count = atomic_read(&mnt->mnt_count) - 1;
+ /* -1 for vfsmount's normal count,
+ * -1 for ref taken in lookup_mnt()
+ */
+ count = atomic_read(&mnt->mnt_count) - 1 - 1;

repeat:
next = this_parent->mnt_mounts.next;
@@ -70,8 +73,14 @@ static int check_vfsmnt(struct vfsmount
int ret = dentry->d_mounted;
struct vfsmount *vfs = lookup_mnt(mnt, dentry);

- if (vfs && is_vfsmnt_tree_busy(vfs))
- ret--;
+ if (vfs) {
+ if (is_vfsmnt_tree_busy(vfs))
+ ret--;
+ /* just to reduce ref count taken in lookup_mnt
+ * cannot call mntput() here
+ */
+ atomic_dec(&vfs->mnt_count);
+ }
DPRINTK(("check_vfsmnt: ret=%d\n", ret));
return ret;
}
_

--
Maneesh Soni
IBM Linux Technology Center,
IBM India Software Lab, Bangalore.
Phone: +91-80-5044999 email: maneesh@in.ibm.com
http://lse.sourceforge.net/
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