On Fri, Dec 01 2017, Shaohua Li wrote: > On Thu, Nov 30, 2017 at 03:26:06PM +1100, Neil Brown wrote: >> On Thu, Nov 30 2017, Guoqing Jiang wrote: >> >> > On 11/30/2017 08:20 AM, NeilBrown wrote: >> >> On Tue, Nov 28 2017, Shaohua Li wrote: >> >> >> >>> On Tue, Nov 28, 2017 at 04:51:25PM +0800, Dennis Yang wrote: >> >>>> Hi, >> >>>> >> >>>> We recently see the following kernel dump on raid1 with some kernel >> >>>> debug option on. >> >>>> >> >>>> <4>[ 40.501369] ------------[ cut here ]------------ >> >>>> <4>[ 40.501375] WARNING: CPU: 7 PID: 7477 at >> >>>> kernel/sched/core.c:7404 __might_sleep+0xa2/0xb0() >> >>>> <4>[ 40.501378] do not call blocking ops when !TASK_RUNNING; state=2 >> >>>> set at [<ffffffff810c28d8>] prepare_to_wait_event+0x58/0x100 >> >>>> <4>[ 40.501379] Modules linked in: dm_c2f(O) pl2303 usbserial >> >>>> qm2_i2c(O) intel_ips drbd(O) flashcache(O) dm_tier_hro_algo >> >>>> dm_thin_pool dm_bio_prison dm_persistent_data hal_netlink(O) k10temp >> >>>> coretemp mlx4_en(O) mlx4_core(O) mlx_compat(O) igb e1000e(O) >> >>>> mpt3sas(O) mpt2sas scsi_transport_sas raid_class usb_storage xhci_pci >> >>>> xhci_hcd usblp uhci_hcd ehci_pci ehci_hcd >> >>>> <4>[ 40.501395] CPU: 7 PID: 7477 Comm: md321_resync Tainted: G >> >>>> O 4.2.8 #1 >> >>>> <4>[ 40.501396] Hardware name: INSYDE QV96/Type2 - Board Product >> >>>> Name1, BIOS QV96IR23 10/21/2015 >> >>>> <4>[ 40.501397] ffffffff8219aff7 ffff880092f7b868 ffffffff81c86c4b >> >>>> ffffffff810dfb59 >> >>>> <4>[ 40.501399] ffff880092f7b8b8 ffff880092f7b8a8 ffffffff81079fa5 >> >>>> ffff880092f7b8e8 >> >>>> <4>[ 40.501401] ffffffff821a4f6d 0000000000000140 0000000000000000 >> >>>> 0000000000000001 >> >>>> <4>[ 40.501403] Call Trace: >> >>>> <4>[ 40.501407] [<ffffffff81c86c4b>] dump_stack+0x4c/0x65 >> >>>> <4>[ 40.501409] [<ffffffff810dfb59>] ? console_unlock+0x279/0x4f0 >> >>>> <4>[ 40.501411] [<ffffffff81079fa5>] warn_slowpath_common+0x85/0xc0 >> >>>> <4>[ 40.501412] [<ffffffff8107a021>] warn_slowpath_fmt+0x41/0x50 >> >>>> <4>[ 40.501414] [<ffffffff810c28d8>] ? prepare_to_wait_event+0x58/0x100 >> >>>> <4>[ 40.501415] [<ffffffff810c28d8>] ? prepare_to_wait_event+0x58/0x100 >> >>>> <4>[ 40.501416] [<ffffffff810a4f72>] __might_sleep+0xa2/0xb0 >> >>>> <4>[ 40.501419] [<ffffffff8117bb7c>] mempool_alloc+0x7c/0x150 >> >>>> <4>[ 40.501422] [<ffffffff8101442a>] ? save_stack_trace+0x2a/0x50 >> >>>> <4>[ 40.501425] [<ffffffff8145b589>] bio_alloc_bioset+0xb9/0x260 >> >>>> <4>[ 40.501428] [<ffffffff816cb6da>] bio_alloc_mddev+0x1a/0x30 >> >>>> <4>[ 40.501429] [<ffffffff816d22a2>] md_super_write+0x32/0x90 >> >>>> <4>[ 40.501431] [<ffffffff816db9b2>] write_page+0x2d2/0x480 >> >>>> <4>[ 40.501432] [<ffffffff816db808>] ? write_page+0x128/0x480 >> >>>> <4>[ 40.501434] [<ffffffff816a45cc>] ? flush_pending_writes+0x1c/0xe0 >> >>>> <4>[ 40.501435] [<ffffffff816dc2a6>] bitmap_unplug+0x156/0x170 >> >>>> <4>[ 40.501437] [<ffffffff810caa2d>] ? trace_hardirqs_on+0xd/0x10 >> >>>> <4>[ 40.501439] [<ffffffff81c94b4b>] ? _raw_spin_unlock_irq+0x2b/0x40 >> >>>> <4>[ 40.501440] [<ffffffff816a4613>] flush_pending_writes+0x63/0xe0 >> >>>> <4>[ 40.501442] [<ffffffff816a4aff>] freeze_array+0x6f/0xc0 >> >>>> <4>[ 40.501443] [<ffffffff810c27e0>] ? wait_woken+0xb0/0xb0 >> >>>> <4>[ 40.501444] [<ffffffff816a4b8f>] raid1_quiesce+0x3f/0x50 >> >>>> <4>[ 40.501446] [<ffffffff816d2254>] md_do_sync+0x1394/0x13b0 >> >>>> <4>[ 40.501447] [<ffffffff816d1531>] ? md_do_sync+0x671/0x13b0 >> >>>> <4>[ 40.501449] [<ffffffff810cb680>] ? __lock_acquire+0x990/0x23a0 >> >>>> <4>[ 40.501451] [<ffffffff810bade7>] ? pick_next_task_fair+0x707/0xc30 >> >>>> <4>[ 40.501453] [<ffffffff8108783c>] ? kernel_sigaction+0x2c/0xc0 >> >>>> <4>[ 40.501455] [<ffffffff81c94b4b>] ? _raw_spin_unlock_irq+0x2b/0x40 >> >>>> <4>[ 40.501456] [<ffffffff816cac80>] ? find_pers+0x80/0x80 >> >>>> <4>[ 40.501457] [<ffffffff816cadbe>] md_thread+0x13e/0x150 >> >>>> <4>[ 40.501458] [<ffffffff816cac80>] ? find_pers+0x80/0x80 >> >>>> <4>[ 40.501460] [<ffffffff816cac80>] ? find_pers+0x80/0x80 >> >>>> <4>[ 40.501462] [<ffffffff8109ded5>] kthread+0x105/0x120 >> >>>> <4>[ 40.501463] [<ffffffff81c94b4b>] ? _raw_spin_unlock_irq+0x2b/0x40 >> >>>> <4>[ 40.501465] [<ffffffff8109ddd0>] ? kthread_create_on_node+0x220/0x220 >> >>>> <4>[ 40.501467] [<ffffffff81c956cf>] ret_from_fork+0x3f/0x70 >> >>>> <4>[ 40.501468] [<ffffffff8109ddd0>] ? kthread_create_on_node+0x220/0x220 >> >>>> <4>[ 40.501469] ---[ end trace bd085fb137be2a87 ]--- >> >>>> >> >>>> It looks like raid1_quiesce() creates a nested sleeping primitives by >> >>>> calling wait_event_lock_irq_cmd() >> >>>> first to change the state to TASK_UNINTERRUPTIBLE and >> >>>> flush_pending_writes() could eventually try >> >>>> to allocate bio for bitmap update with GFP_NOIO which might sleep and >> >>>> triggers this warning. >> >>>> I am not sure if this warning is just a false-positive or should we >> >>>> change the bio allocation >> >>>> gfp flag to GFP_NOWAIT to prevent it from blocking? >> >>> This is a legit warnning. Changing gfp to GFP_NOWAIT doesn't completely fix the >> >>> issue, because generic_make_request could sleep too. I think we should move the >> >>> work to a workqueue. Could you please try below patch (untested yet)? >> >> I think it would be simpler to call __set_current_state(TASK_RUNNING) >> >> in the 'then' branch of flush_pending_writes(). >> > >> > There is no 'then' branch in this function, maybe you mean set >> > TASK_RUNNING in the 'if' branch, >> > since the calltrace is triggered by flush_pending_writes -> >> > flush_bio_list -> bitmap_unplug. >> >> I grew up with BASIC and Pascal. >> Every "if" statement has a "then" branch and an "else" branch. >> The fact that C doesn't have a "then" keyword doesn't mean there isn't a >> 'then' branch. >> >> But yes, state should be set to TASK_RUNNING when the condition in the >> 'if' statement evaluates as 'true' (or maybe I should say "doesn't >> evaluate to 0"). > > Completely agree this fixes the issue, but I'm a little hesitant to apply it. > It looks a little weird, I mean, at least I must add comments to explain why we > do that way. Do you have strong preference to do this way? My preference is quite strong. I believe the current code is simple and correct and doesn't need to change. The warning is a false positive. It is a good warning to have, but in this case it doesn't indicate a problem. I agree that comments are a good thing here. So I propose this patch, replete with comments. Thanks, NeilBrown Subject: [PATCH] md/raid1,raid10: silence warning about wait-within-wait If you prepare_to_wait() after a previous prepare_to_wait(), but before calling schedule(), you get warning: do not call blocking ops when !TASK_RUNNING; state=2 This is appropriate as it is often a bug. The event that the first prepare_to_wait() expects might wake up the schedule following the second prepare_to_wait(), which could be confusing. However if both prepare_to_wait()s are part of simple wait_event() loops, and if the inner one is rarely called, then there is no problem. The inner loop is too simple to get confused by a stray wakeup, and the outer loop won't spin unduly because the inner doesnt affect it often. This pattern occurs in both raid1.c and raid10.c in the use of flush_pending_writes(). The warning can be silenced by setting current->state to TASK_RUNNING. Signed-off-by: NeilBrown <neilb@xxxxxxxx> --- drivers/md/raid1.c | 11 +++++++++++ drivers/md/raid10.c | 11 +++++++++++ 2 files changed, 22 insertions(+) diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index cc9d337a1ed3..0faec3a5f017 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -813,6 +813,17 @@ static void flush_pending_writes(struct r1conf *conf) bio = bio_list_get(&conf->pending_bio_list); conf->pending_count = 0; spin_unlock_irq(&conf->device_lock); + + /* As this is called in a wait_event() loop, current->state + * might be TASK_UNINTERRUPTIBLE which will cause a warning + * when we prepare to wait again. + * As it is rare that this path is taken, it is perfectly + * safe to force us to go around the wait_event() loop + * again, so the warning is a false-positive. + * Silence the warning by resetting thread state + */ + __set_current_state(TASK_RUNNING); + flush_bio_list(conf, bio); } else spin_unlock_irq(&conf->device_lock); diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index b9edbc747a95..df7b78a79735 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -898,6 +898,17 @@ static void flush_pending_writes(struct r10conf *conf) bio = bio_list_get(&conf->pending_bio_list); conf->pending_count = 0; spin_unlock_irq(&conf->device_lock); + + /* As this is called in a wait_event() loop, current->state + * might be TASK_UNINTERRUPTIBLE which will cause a warning + * when we prepare to wait again. + * As it is rare that this path is taken, it is perfectly + * safe to force us to go around the wait_event() loop + * again, so the warning is a false-positive. + * Silence the warning by resetting thread state + */ + __set_current_state(TASK_RUNNING); + /* flush any pending bitmap writes to disk * before proceeding w/ I/O */ bitmap_unplug(conf->mddev->bitmap); -- 2.14.0.rc0.dirty
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