From: Zhang Xiaoxu zhangxiaoxu5@huawei.com
commit fcb170a9d825d7db4a3fb870b0300f5a40a8d096 upstream.
The 'queue->nr' will wraparound from 0 to 255 when only current priority queue has tasks. This maybe lead a deadlock same as commit dfe1fe75e00e ("NFSv4: Fix deadlock between nfs4_evict_inode() and nfs4_opendata_get_inode()"):
Privileged delegreturn task is queued to privileged list because all the slots are assigned. When non-privileged task complete and release the slot, a non-privileged maybe picked out. It maybe allocate slot failed when the session on draining.
If the 'queue->nr' has wraparound to 255, and no enough slot to service it, then the privileged delegreturn will lost to wake up.
So we should avoid the wraparound on 'queue->nr'.
Reported-by: Hulk Robot hulkci@huawei.com Fixes: 5fcdfacc01f3 ("NFSv4: Return delegations synchronously in evict_inode") Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Zhang Xiaoxu zhangxiaoxu5@huawei.com Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/sunrpc/sched.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -476,7 +476,8 @@ static struct rpc_task *__rpc_find_next_ * Service a batch of tasks from a single owner. */ q = &queue->tasks[queue->priority]; - if (!list_empty(q) && --queue->nr) { + if (!list_empty(q) && queue->nr) { + queue->nr--; task = list_first_entry(q, struct rpc_task, u.tk_wait.list); goto out; }