NLM sometimes gets burnt by implementations of f_op->lock for F_GETLK
modifying the lock structure (swapping out fl_owner) when the return is
F_UNLCK.
Yes, NLM should be more defensive, but perhaps we should be checking for
everyone, as per POSIX "If no lock is found that would prevent this lock
from being created, then the structure shall be left unchanged except
for
the lock type which shall be set to F_UNLCK."
That would save others from the pain, as the offenders would hopefully
take
notice.
Something like:
diff --git a/fs/locks.c b/fs/locks.c
index 32c948fe2944..4cc425008036 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2274,8 +2274,16 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned
int, cmd)
*/
int vfs_test_lock(struct file *filp, struct file_lock *fl)
{
- if (filp->f_op->lock)
- return filp->f_op->lock(filp, F_GETLK, fl);
+ int ret;
+ fl_owner_t test_owner = fl->fl_owner;
+
+ if (filp->f_op->lock) {
+ ret = filp->f_op->lock(filp, F_GETLK, fl);
+ if (fl->fl_type == F_UNLCK)
+ WARN_ON(fl->fl_owner != test_owner);
+ return ret;
+ }
+
posix_test_lock(filp, fl);
return 0;
}
.. I'm worried that might be too big of a hammer though. Any thoughts?
Ben
