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| author | Al Viro <viro@ZenIV.linux.org.uk> | 2009-02-16 03:38:12 +0100 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-02-17 23:02:08 +0100 |
| commit | 1a88b5364b535edaa321d70a566e358390ff0872 (patch) | |
| tree | 41c557358a595de85ba8a7a7697901ff21d1de1a | |
| parent | Linux 2.6.29-rc5 (diff) | |
| download | linux-1a88b5364b535edaa321d70a566e358390ff0872.tar.xz linux-1a88b5364b535edaa321d70a566e358390ff0872.zip | |
Fix incomplete __mntput locking
Getting this wrong caused
WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2()
due to optimistically checking cpu_writer->mnt outside the spinlock.
Here's what we really want:
* we know that nobody will set cpu_writer->mnt to mnt from now on
* all changes to that sucker are done under cpu_writer->lock
* we want the laziest equivalent of
spin_lock(&cpu_writer->lock);
if (likely(cpu_writer->mnt != mnt)) {
spin_unlock(&cpu_writer->lock);
continue;
}
/* do stuff */
that would make sure we won't miss earlier setting of ->mnt done by
another CPU.
Anyway, for now we just move the spin_lock() earlier and move the test
into the properly locked region.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reported-and-tested-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | fs/namespace.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index 228d8c4bfd18..06f8e63f6cb1 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -614,9 +614,11 @@ static inline void __mntput(struct vfsmount *mnt) */ for_each_possible_cpu(cpu) { struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu); - if (cpu_writer->mnt != mnt) - continue; spin_lock(&cpu_writer->lock); + if (cpu_writer->mnt != mnt) { + spin_unlock(&cpu_writer->lock); + continue; + } atomic_add(cpu_writer->count, &mnt->__mnt_writers); cpu_writer->count = 0; /* |