From mboxrd@z Thu Jan 1 00:00:00 1970 From: Coly Li Subject: [PATCH v1 02/10] bcache: set task properly in allocator_wait() Date: Wed, 3 Jan 2018 22:03:17 +0800 Message-ID: <20180103140325.63175-3-colyli@suse.de> References: <20180103140325.63175-1-colyli@suse.de> Return-path: Received: from mx2.suse.de ([195.135.220.15]:54958 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752247AbeACODy (ORCPT ); Wed, 3 Jan 2018 09:03:54 -0500 In-Reply-To: <20180103140325.63175-1-colyli@suse.de> Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org Cc: linux-block@vger.kernel.org, mlyle@lyle.org, tang.junhui@zte.com.cn, Coly Li Kernel thread routine bch_allocator_thread() references macro allocator_wait() to wait for a condition or quit to do_exit() when kthread_should_stop() is true. Macro allocator_wait() has 2 issues in setting task state, let's see its code piece, 284 while (1) { \ 285 set_current_state(TASK_INTERRUPTIBLE); \ 286 if (cond) \ 287 break; \ 288 \ 289 mutex_unlock(&(ca)->set->bucket_lock); \ 290 if (kthread_should_stop()) \ 291 return 0; \ 292 \ 293 schedule(); \ 294 mutex_lock(&(ca)->set->bucket_lock); \ 295 } \ 296 __set_current_state(TASK_RUNNING); \ 1) At line 285, task state is set to TASK_INTERRUPTIBLE, if at line 290 kthread_should_stop() is true, the kernel thread will terminate and return to kernel/kthread.s:kthread(), then calls do_exit() with TASK_INTERRUPTIBLE state. This is not a suggested behavior and a warning message will be reported by might_sleep() in do_exit() code path: "WARNING: do not call blocking ops when !TASK_RUNNING; state=1 set at [xxxx]". 2) Because task state is set to TASK_INTERRUPTIBLE at line 285, when break while-loop the task state has to be set back to TASK_RUNNING at line 296. Indeed it is unncessary, if task state is set to TASK_INTERRUPTIBLE before calling schedule() at line 293, we don't need to set the state back to TASK_RUNNING at line 296 anymore. The reason is, allocator kthread is only woken up by wake_up_process(), this routine makes sure the task state of allocator kthread will be TASK_RUNNING after it returns from schedule() at line 294 (see kernel/sched/core.c:try_to_wake_up() for more detailed information). This patch fixes the above 2 issues by, 1) Setting TASK_INTERRUPTIBLE state just before calling schedule(). 2) Then setting TASK_RUNNING at line 296 is unnecessary, remove it. Signed-off-by: Coly Li --- drivers/md/bcache/alloc.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c index a0cc1bc6d884..48c002faf08d 100644 --- a/drivers/md/bcache/alloc.c +++ b/drivers/md/bcache/alloc.c @@ -282,7 +282,6 @@ static void invalidate_buckets(struct cache *ca) #define allocator_wait(ca, cond) \ do { \ while (1) { \ - set_current_state(TASK_INTERRUPTIBLE); \ if (cond) \ break; \ \ @@ -290,10 +289,10 @@ do { \ if (kthread_should_stop()) \ return 0; \ \ + set_current_state(TASK_INTERRUPTIBLE); \ schedule(); \ mutex_lock(&(ca)->set->bucket_lock); \ } \ - __set_current_state(TASK_RUNNING); \ } while (0) static int bch_allocator_push(struct cache *ca, long bucket) -- 2.15.1