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    Subject[PATCH 5.13 067/800] SUNRPC: Fix the batch tasks count wraparound.
    Date
    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
    @@ -595,7 +595,8 @@ 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;
    }

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