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>
1 file changed