"Panic: unable to handle kernel page request" in posix_unblock_lock() called from nfs4_laundromat()

Dear Developers:

OK, I have attached the patch.

Sorry, I have the only handwriting memo of console messages. Maybe useless, but I also attach its scanned copy.

Sincerely yours
Naofumi Honda

*** linux-4.9.60/fs/nfsd/nfs4state.c.org 2017-11-09 09:49:11.071026183 +0900
--- linux-4.9.60/fs/nfsd/nfs4state.c 2017-11-09 09:51:36.370697280 +0900
***************
*** 4677,4683 ****
spin_unlock(&nn->blocked_locks_lock);

while (!list_empty(&reaplist)) {
! nbl = list_first_entry(&nn->blocked_locks_lru,
struct nfsd4_blocked_lock, nbl_lru);
list_del_init(&nbl->nbl_lru); posix_unblock_lock(&nbl->nbl_lock);
--- 4677,4683 ----
spin_unlock(&nn->blocked_locks_lock);

while (!list_empty(&reaplist)) {
! nbl = list_first_entry(&reaplist,
struct nfsd4_blocked_lock, nbl_lru);
list_del_init(&nbl->nbl_lru); posix_unblock_lock(&nbl->nbl_lock);
***************
*** 7071,7077 ****
spin_unlock(&nn->blocked_locks_lock);

while (!list_empty(&reaplist)) {
! nbl = list_first_entry(&nn->blocked_locks_lru,
struct nfsd4_blocked_lock, nbl_lru);
list_del_init(&nbl->nbl_lru); posix_unblock_lock(&nbl->nbl_lock);
--- 7071,7077 ----
spin_unlock(&nn->blocked_locks_lock);

while (!list_empty(&reaplist)) {
! nbl = list_first_entry(&reaplist,
struct nfsd4_blocked_lock, nbl_lru);
list_del_init(&nbl->nbl_lru); posix_unblock_lock(&nbl->nbl_lock);

Thanks for the investigation and the fix!

For future reference, we prefer patches to be inline with the email message (not attached), and prefer them in "unified" format.

But for a one-off patch I can fix it up myself; applied as follows.

--b.

commit c26806a20fa3

Author: Naofumi Honda <[email protected]>
Date:   Thu Nov 9 10:57:16 2017 -0500

nfsd: fix panic in posix_unblock_lock called from nfs4_laundromat

From kernel 4.9, my two nfsv4 servers sometimes suffer from
"panic: unable to handle kernel page request"
in posix_unblock_lock() called from nfs4_laundromat().

These panics diseappear if we revert the commit "nfsd: add a LRU list for blocked locks".

The cause appears to be a typo in nfs4_laundromat(), which is also present in nfs4_state_shutdown_net().

index 923243369bbc..b99830ab63aa 100644
@@ -4791,7 +4791,7 @@ nfs4_laundromat(struct nfsd_net *nn)
 	spin_unlock(&nn->blocked_locks_lock);
 
 	while (!list_empty(&reaplist)) {
-		nbl = list_first_entry(&nn->blocked_locks_lru,
+		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
 		list_del_init(&nbl->nbl_lru);
 		posix_unblock_lock(&nbl->nbl_lock);

@@ -7260,7 +7260,7 @@ nfs4_state_shutdown_net(struct net *net)
 	spin_unlock(&nn->blocked_locks_lock);
 
 	while (!list_empty(&reaplist)) {
-		nbl = list_first_entry(&nn->blocked_locks_lru,
+		nbl = list_first_entry(&reaplist,
 					struct nfsd4_blocked_lock, nbl_lru);
 		list_del_init(&nbl->nbl_lru);
 		posix_unblock_lock(&nbl->nbl_lock);