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Message-ID: <20180409001936.162706-136-alexander.levin@microsoft.com> Date: Mon, 9 Apr 2018 00:21:44 +0000 From: Sasha Levin <Alexander.Levin@...rosoft.com> To: "stable@...r.kernel.org" <stable@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> CC: Coly Li <colyli@...e.de>, Michael Lyle <mlyle@...e.org>, Junhui Tang <tang.junhui@....com.cn>, Jens Axboe <axboe@...nel.dk>, Sasha Levin <Alexander.Levin@...rosoft.com> Subject: [PATCH AUTOSEL for 4.14 136/161] bcache: properly set task state in bch_writeback_thread() From: Coly Li <colyli@...e.de> [ Upstream commit 99361bbf26337186f02561109c17a4c4b1a7536a ] Kernel thread routine bch_writeback_thread() has the following code block, 447 down_write(&dc->writeback_lock); 448~450 if (check conditions) { 451 up_write(&dc->writeback_lock); 452 set_current_state(TASK_INTERRUPTIBLE); 453 454 if (kthread_should_stop()) 455 return 0; 456 457 schedule(); 458 continue; 459 } If condition check is true, its task state is set to TASK_INTERRUPTIBLE and call schedule() to wait for others to wake up it. There are 2 issues in current code, 1, Task state is set to TASK_INTERRUPTIBLE after the condition checks, if another process changes the condition and call wake_up_process(dc-> writeback_thread), then at line 452 task state is set back to TASK_INTERRUPTIBLE, the writeback kernel thread will lose a chance to be waken up. 2, At line 454 if kthread_should_stop() is true, writeback kernel thread will return to kernel/kthread.c:kthread() with TASK_INTERRUPTIBLE and call do_exit(). It is not good to enter do_exit() with task state TASK_INTERRUPTIBLE, in following code path might_sleep() is called and a warning message is reported by __might_sleep(): "WARNING: do not call blocking ops when !TASK_RUNNING; state=1 set at [xxxx]". For the first issue, task state should be set before condition checks. Ineed because dc->writeback_lock is required when modifying all the conditions, calling set_current_state() inside code block where dc-> writeback_lock is hold is safe. But this is quite implicit, so I still move set_current_state() before all the condition checks. For the second issue, frankley speaking it does not hurt when kernel thread exits with TASK_INTERRUPTIBLE state, but this warning message scares users, makes them feel there might be something risky with bcache and hurt their data. Setting task state to TASK_RUNNING before returning fixes this problem. In alloc.c:allocator_wait(), there is also a similar issue, and is also fixed in this patch. Changelog: v3: merge two similar fixes into one patch v2: fix the race issue in v1 patch. v1: initial buggy fix. Signed-off-by: Coly Li <colyli@...e.de> Reviewed-by: Hannes Reinecke <hare@...e.de> Reviewed-by: Michael Lyle <mlyle@...e.org> Cc: Michael Lyle <mlyle@...e.org> Cc: Junhui Tang <tang.junhui@....com.cn> Signed-off-by: Jens Axboe <axboe@...nel.dk> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com> --- drivers/md/bcache/alloc.c | 4 +++- drivers/md/bcache/writeback.c | 7 +++++-- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c index 934b1fce4ce1..02b576d55758 100644 --- a/drivers/md/bcache/alloc.c +++ b/drivers/md/bcache/alloc.c @@ -287,8 +287,10 @@ do { \ break; \ \ mutex_unlock(&(ca)->set->bucket_lock); \ - if (kthread_should_stop()) \ + if (kthread_should_stop()) { \ + set_current_state(TASK_RUNNING); \ return 0; \ + } \ \ schedule(); \ mutex_lock(&(ca)->set->bucket_lock); \ diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 70454f2ad2fa..f046dedc59ab 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -420,18 +420,21 @@ static int bch_writeback_thread(void *arg) while (!kthread_should_stop()) { down_write(&dc->writeback_lock); + set_current_state(TASK_INTERRUPTIBLE); if (!atomic_read(&dc->has_dirty) || (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) && !dc->writeback_running)) { up_write(&dc->writeback_lock); - set_current_state(TASK_INTERRUPTIBLE); - if (kthread_should_stop()) + if (kthread_should_stop()) { + set_current_state(TASK_RUNNING); return 0; + } schedule(); continue; } + set_current_state(TASK_RUNNING); searched_full_index = refill_dirty(dc); -- 2.15.1
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