From: Pavel Begunkov asml.silence@gmail.com
commit 1d5f5ea7cb7d15b9fb1cc82673ebb054f02cd7d2 upstream.
INFO: task iou-wrk-6609:6612 blocked for more than 143 seconds. Not tainted 5.15.0-rc5-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:iou-wrk-6609 state:D stack:27944 pid: 6612 ppid: 6526 flags:0x00004006 Call Trace: context_switch kernel/sched/core.c:4940 [inline] __schedule+0xb44/0x5960 kernel/sched/core.c:6287 schedule+0xd3/0x270 kernel/sched/core.c:6366 schedule_timeout+0x1db/0x2a0 kernel/time/timer.c:1857 do_wait_for_common kernel/sched/completion.c:85 [inline] __wait_for_common kernel/sched/completion.c:106 [inline] wait_for_common kernel/sched/completion.c:117 [inline] wait_for_completion+0x176/0x280 kernel/sched/completion.c:138 io_worker_exit fs/io-wq.c:183 [inline] io_wqe_worker+0x66d/0xc40 fs/io-wq.c:597 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
io-wq worker may submit a task_work to the master task and upon io_worker_exit() wait for the tw to get executed. The problem appears when the master task is waiting in coredump.c:
468 freezer_do_not_count(); 469 wait_for_completion(&core_state->startup); 470 freezer_count();
Apparently having some dependency on children threads getting everything stuck. Workaround it by cancelling the taks_work callback that causes it before going into io_worker_exit() waiting.
p.s. probably a better option is to not submit tw elevating the refcount in the first place, but let's leave this excercise for the future.
Cc: stable@vger.kernel.org Reported-and-tested-by: syzbot+27d62ee6f256b186883e@syzkaller.appspotmail.com Signed-off-by: Pavel Begunkov asml.silence@gmail.com Link: https://lore.kernel.org/r/142a716f4ed936feae868959059154362bfa8c19.163550945... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/io-wq.c | 46 +++++++++++++++++++++++++++++++++++++--------- 1 file changed, 37 insertions(+), 9 deletions(-)
--- a/fs/io-wq.c +++ b/fs/io-wq.c @@ -140,6 +140,7 @@ static void io_wqe_dec_running(struct io static bool io_acct_cancel_pending_work(struct io_wqe *wqe, struct io_wqe_acct *acct, struct io_cb_cancel_data *match); +static void create_worker_cb(struct callback_head *cb);
static bool io_worker_get(struct io_worker *worker) { @@ -174,9 +175,44 @@ static void io_worker_ref_put(struct io_ complete(&wq->worker_done); }
+static void io_worker_cancel_cb(struct io_worker *worker) +{ + struct io_wqe_acct *acct = io_wqe_get_acct(worker); + struct io_wqe *wqe = worker->wqe; + struct io_wq *wq = wqe->wq; + + atomic_dec(&acct->nr_running); + raw_spin_lock(&worker->wqe->lock); + acct->nr_workers--; + raw_spin_unlock(&worker->wqe->lock); + io_worker_ref_put(wq); + clear_bit_unlock(0, &worker->create_state); + io_worker_release(worker); +} + +static bool io_task_worker_match(struct callback_head *cb, void *data) +{ + struct io_worker *worker; + + if (cb->func != create_worker_cb) + return false; + worker = container_of(cb, struct io_worker, create_work); + return worker == data; +} + static void io_worker_exit(struct io_worker *worker) { struct io_wqe *wqe = worker->wqe; + struct io_wq *wq = wqe->wq; + + while (1) { + struct callback_head *cb = task_work_cancel_match(wq->task, + io_task_worker_match, worker); + + if (!cb) + break; + io_worker_cancel_cb(worker); + }
if (refcount_dec_and_test(&worker->ref)) complete(&worker->ref_done); @@ -1150,17 +1186,9 @@ static void io_wq_exit_workers(struct io
while ((cb = task_work_cancel_match(wq->task, io_task_work_match, wq)) != NULL) { struct io_worker *worker; - struct io_wqe_acct *acct;
worker = container_of(cb, struct io_worker, create_work); - acct = io_wqe_get_acct(worker); - atomic_dec(&acct->nr_running); - raw_spin_lock(&worker->wqe->lock); - acct->nr_workers--; - raw_spin_unlock(&worker->wqe->lock); - io_worker_ref_put(wq); - clear_bit_unlock(0, &worker->create_state); - io_worker_release(worker); + io_worker_cancel_cb(worker); }
rcu_read_lock();