Patch from Neil Brown <neilb@cse.unsw.edu.au>
Fix deadlock problem in lockd.
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.
fs/lockd/svclock.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)
diff -puN fs/lockd/svclock.c~lockd-lockup-fix-2 fs/lockd/svclock.c
--- 25/fs/lockd/svclock.c~lockd-lockup-fix-2 2003-02-25 20:02:34.000000000 -0800
+++ 25-akpm/fs/lockd/svclock.c 2003-02-25 20:02:34.000000000 -0800
@@ -305,8 +305,6 @@ 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);
@@ -314,6 +312,9 @@ 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);
@@ -346,7 +347,10 @@ 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
+ * 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;
_