[PATCH] Fix deadlock problem in lockd.

[PATCH] Fix deadlock problem in lockd.

[NeilBrown]

nlmsvc_lock calls nlmsvc_create_block with file->f_sema
held.
nlmsvc_create_block calls nlmclnt_lookup_host which might
call nlm_gc_hosts which might, eventually, try to claim
file->f_sema for the same file -> deadlock.

nlmsvc_create_block does not need any protection under
any lock as lockd is single-threaded and _create_block
only plays with internal data structures.

So we release the f_sema before calling in, and make sure
it gets claimed again afterwards.

(This was fixed in 2.5 8 months ago)


diff ./fs/lockd/svclock.c~current~ ./fs/lockd/svclock.c
--- ./fs/lockd/svclock.c~current~	2003-10-29 09:07:10.000000000 +1100
+++ ./fs/lockd/svclock.c	2003-10-29 09:07:10.000000000 +1100
@@ -317,8 +317,6 @@ nlmsvc_lock(struct svc_rqst *rqstp, stru
 				(long long)lock->fl.fl_end,
 				wait);
 
-	/* Lock file against concurrent access */
-	down(&file->f_sema);
 
 	/* Get existing block (in case client is busy-waiting) */
 	block = nlmsvc_lookup_block(file, lock, 0);
@@ -326,6 +324,9 @@ nlmsvc_lock(struct svc_rqst *rqstp, stru
 	lock->fl.fl_flags |= FL_LOCKD;
 
 again:
+	/* Lock file against concurrent access */
+	down(&file->f_sema);
+
 	if (!(conflock = posix_test_lock(&file->f_file, &lock->fl))) {
 		error = posix_lock_file(&file->f_file, &lock->fl, 0);
 
@@ -358,7 +359,10 @@ again:
 
 	/* If we don't have a block, create and initialize it. Then
 	 * retry because we may have slept in kmalloc. */
+	/* We have to release f_sema as nlmsvc_create_block may try to
+	 * claim it while doing host garbage collection */
 	if (block == NULL) {
+		up(&file->f_sema);
 		dprintk("lockd: blocking on this lock (allocating).\n");
 		if (!(block = nlmsvc_create_block(rqstp, file, lock, cookie)))
 			return nlm_lck_denied_nolocks;


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