nbd: fix circular lock dependency in nbd_reconnect_socket#1020
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nbd: fix circular lock dependency in nbd_reconnect_socket#1020blktests-ci[bot] wants to merge 1 commit into
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Upstream branch: 4edcdef |
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Upstream branch: dc59e4f |
Move sk_set_memalloc() out of the tx_lock critical section in
nbd_reconnect_socket() to break a circular lock dependency.
sk_set_memalloc() internally calls static_branch_inc() which acquires
cpu_hotplug_lock. When called under tx_lock, this creates the dependency:
tx_lock -> cpu_hotplug_lock
The lockdep splat shows the following circular chain:
cmd->lock -> tx_lock
from nbd_queue_rq() in the block I/O dispatch path.
tx_lock -> cpu_hotplug_lock
from nbd_reconnect_socket() calling sk_set_memalloc() under tx_lock.
cpu_hotplug_lock -> fs_reclaim -> q_usage_counter(io)
from create_worker() during CPU hotplug needing memory allocation,
which depends on block I/O completion to reclaim memory.
q_usage_counter(io) -> elevator_lock
from nbd_start_device() -> blk_mq_update_nr_hw_queues() ->
elevator_change() which freezes the queue then acquires elevator_lock.
elevator_lock -> set->srcu -> cmd->lock
from elevator_switch() -> blk_mq_quiesce_queue() waiting for srcu,
which waits for the I/O dispatch path holding cmd->lock.
Fix this by moving sk_set_memalloc() and sk_sndtimeo setup before the
tx_lock acquisition. This is safe because the new socket has not yet
been assigned to nsock->sock and is invisible to other code paths. In
the failure path (no dead connection found), sk_clear_memalloc() is
called to undo the setup before releasing the socket.
Fixes: b7aa3d3 ("nbd: add a reconfigure netlink command")
Reported-by: syzbot+3dbc6142c85cc77eaf04@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3dbc6142c85cc77eaf04
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
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Pull request for series with
subject: nbd: fix circular lock dependency in nbd_reconnect_socket
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1117874