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Sun, 8 Apr 2018 20:39:23 -0400 From: Sasha Levin To: "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: Coly Li , Michael Lyle , Junhui Tang , Jens Axboe , Sasha Levin Subject: [PATCH AUTOSEL for 4.4 155/162] bcache: properly set task state in bch_writeback_thread() Thread-Topic: [PATCH AUTOSEL for 4.4 155/162] bcache: properly set task state in bch_writeback_thread() Thread-Index: AQHTz5nfN4m4EbvFHk2L7GEmV0MVqw== Date: Mon, 9 Apr 2018 00:29:51 +0000 Message-ID: <20180409002738.163941-155-alexander.levin@microsoft.com> References: <20180409002738.163941-1-alexander.levin@microsoft.com> In-Reply-To: <20180409002738.163941-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR2101MB1125;7:ePyOlG1A2lXS9tqY17jZlVWs3YlDjUuU7YNH9KNQZm07ZyCS7/A/SelzS0/1bY4mFKv9c4UFbAgaP5Ii1/qcwaZeg5Zw337zyCOeIqyXk0CzZKdJJfCfoM1CtEHia6ZezkI6W6t1lt9BA8/stGhImlmOn/UP1tm1sMaII8zhxBslOeiKD+MAPvdWa0WHc3OkhTv/U6vlgHLvGJYGpkaSMzPYiq8NAmwnDNQZyAQkKCVY4OippLH38MqoubFjTRdY;20:/X6VKNV7qjhNGK8tl/E8ONQ1sWafwWNh43jcsPPUX/W2HkHQKBskD+9kfXu/Mnw6dJR+mEOS2Kwqak615wG8fFafP+wVOGB6nuYsSgkiGusqlq0AfL9OFW137Lzp4alWjwZPSaZbwsVyCDBH4ZGBaCfejnIGAcPOcy32jIlfsH0= X-MS-Office365-Filtering-Correlation-Id: a550832e-c8ae-46a5-3d28-08d59db2551f x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(4534165)(4627221)(201703031133081)(201702281549075)(5600026)(4604075)(3008032)(48565401081)(2017052603328)(7193020);SRVR:DM5PR2101MB1125; 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x-microsoft-antispam-message-info: 8NvGe7X71UiykWAP9jL/zcGkvDqP3Xonlrvz5KeQCG40OH7468iIhURDbs3YeOsbNjRm9pZCerC+0lYYEn28Hp890pPz8mpq/K63uZcjz1ASfcL7eRd2YSnYWGqZouqMnCcIJpeW6lQMLmd4zoDMzOlUmeinXl70v1BKuZfuP3+ZDROVLw7kXDVU2w+cHr0yeG/27osw1e6KHU3QSaV8mEuXjfPZ9GniT+b9VEeIQep2fQ5XfhM46RDxdhbiSfLr4aPU0aiVSHXznBl6PmxMKp4DWHd24fiD8sq2gbQb1g9BrKK5gErppog+TLFcM9aooOV9bAGHx9v5Us/tBXVdZVbFKTP20ijDycUdawzsKh32w6Hok/VnVhfB+Iuq4V87gOlETG8iknUTMMDFaajSbQzjxyD4agN/veRTAquPYCw= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: a550832e-c8ae-46a5-3d28-08d59db2551f X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Apr 2018 00:29:51.1621 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB1125 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Coly Li [ 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=3D1 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 Reviewed-by: Hannes Reinecke Reviewed-by: Michael Lyle Cc: Michael Lyle Cc: Junhui Tang Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- 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 4d46f2ce606f..3263658ccedb 100644 --- a/drivers/md/bcache/alloc.c +++ b/drivers/md/bcache/alloc.c @@ -285,8 +285,10 @@ do { \ break; \ \ mutex_unlock(&(ca)->set->bucket_lock); \ - if (kthread_should_stop()) \ + if (kthread_should_stop()) { \ + set_current_state(TASK_RUNNING); \ return 0; \ + } \ \ try_to_freeze(); \ schedule(); \ diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index bbb1dc9e1639..4639270bf99b 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -425,19 +425,22 @@ static int bch_writeback_thread(void *arg) =20 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); =20 - if (kthread_should_stop()) + if (kthread_should_stop()) { + set_current_state(TASK_RUNNING); return 0; + } =20 try_to_freeze(); schedule(); continue; } + set_current_state(TASK_RUNNING); =20 searched_full_index =3D refill_dirty(dc); =20 --=20 2.15.1