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Date:	Mon, 22 Dec 2014 13:12:12 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Fam Zheng <famz@...hat.com>
Cc:	Benjamin LaHaise <bcrl@...ck.org>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [v3.19-rc1] read_events => aio_read_events => WARNING: "do not call blocking ops when !TASK_RUNNING"

Hello,

I got this warning on v3.19-rc1:

[   16.325814] ------------[ cut here ]------------
[   16.325832] WARNING: CPU: 0 PID: 3368 at kernel/sched/core.c:7303 __might_sleep+0x55/0x94()
[   16.325839] do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff81071360>] prepare_to_wait_event+0x8c/0xd8
[   16.325843] Modules linked in: xt_multiport xt_addrtype xt_conntrack ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack bridge dm_thin_pool dm_persistent_data crc32c_generic libcrc32c dm_bio_prison dm_bufio dm_mod iptable_filter ip_tables bnep xt_hl nf_log_ipv6 nf_log_common xt_LOG binfmt_misc ip6table_filter ip6_tables x_tables nfsd nfs_acl nfs lockd grace fscache sunrpc 8021q garp mrp stp llc tun fuse loop iTCO_wdt iTCO_vendor_support snd_hda_codec_conexant snd_hda_codec_generic coretemp arc4 kvm_intel kvm ecb evdev psmouse serio_raw uvcvideo videobuf2_vmalloc videobuf2_memops cdc_mbim cdc_wdm cdc_ncm videobuf2_core v4l2_common usbnet mii cdc_acm videodev iwlmvm btusb mac80211 bluetooth iwlwifi snd_hda_intel i2c_i801 snd_hda_controller
[   16.325980]  lpc_ich mfd_core cfg80211 snd_hda_codec snd_hwdep snd_pcm_oss snd_mixer_oss snd_pcm snd_timer thinkpad_acpi wmi nvram snd soundcore rfkill ac i915 battery i2c_algo_bit drm_kms_helper video drm button acpi_cpufreq processor ext4 crc16 jbd2 mbcache nbd microcode sg sr_mod sd_mod cdrom ahci libahci libata scsi_mod e1000e ehci_pci uhci_hcd ehci_hcd ptp usbcore usb_common pps_core thermal thermal_sys
[   16.326070] CPU: 0 PID: 3368 Comm: mysqld Not tainted 3.19.0-rc1 #270
[   16.326074] Hardware name: LENOVO 2776LEG/2776LEG, BIOS 6EET55WW (3.15 ) 12/19/2011
[   16.326077]  0000000000000009 ffff88022a66fc58 ffffffff813cf430 0000000000000000
[   16.326087]  ffff88022a66fca8 ffff88022a66fc98 ffffffff8104117c 00000000000092e8
[   16.326095]  ffffffff81060e84 ffffffff815a5241 000000000000026d 0000000000000000
[   16.326104] Call Trace:
[   16.326112]  [<ffffffff813cf430>] dump_stack+0x4c/0x65
[   16.326119]  [<ffffffff8104117c>] warn_slowpath_common+0x9c/0xb6
[   16.326126]  [<ffffffff81060e84>] ? __might_sleep+0x55/0x94
[   16.326132]  [<ffffffff8104122a>] warn_slowpath_fmt+0x41/0x43
[   16.326141]  [<ffffffff8100a3cd>] ? native_sched_clock+0x35/0x37
[   16.326147]  [<ffffffff81071360>] ? prepare_to_wait_event+0x8c/0xd8
[   16.326153]  [<ffffffff81071360>] ? prepare_to_wait_event+0x8c/0xd8
[   16.326159]  [<ffffffff81060e84>] __might_sleep+0x55/0x94
[   16.326166]  [<ffffffff813d3205>] mutex_lock_nested+0x2a/0x39e
[   16.326173]  [<ffffffff81070db9>] ? spin_unlock_irqrestore+0x9/0xb
[   16.326180]  [<ffffffff81067f61>] ? local_clock+0x19/0x22
[   16.326187]  [<ffffffff81076446>] ? lock_release_holdtime.part.26+0x71/0x7f
[   16.326194]  [<ffffffff813d514e>] ? _raw_spin_unlock_irqrestore+0x3a/0x48
[   16.326201]  [<ffffffff8117691f>] aio_read_events+0x45/0x282
[   16.326208]  [<ffffffff81176fe0>] read_events+0x1c0/0x23c
[   16.326214]  [<ffffffff8107124d>] ? abort_exclusive_wait+0x95/0x95
[   16.326221]  [<ffffffff81095193>] ? hrtimer_get_res+0x47/0x47
[   16.326227]  [<ffffffff81095c9e>] ? hrtimer_start_range_ns+0xf/0x11
[   16.326234]  [<ffffffff81178d62>] SyS_io_getevents+0x4c/0x76
[   16.326241]  [<ffffffff813d5492>] system_call_fastpath+0x12/0x17
[   16.326246] ---[ end trace aa79768e2e6ba68a ]---


And the mysqld process just sits there burning CPU:

top - 13:01:23 up 33 min, 15 users,  load average: 10.07, 10.23, 9.28
Tasks: 175 total,   2 running, 173 sleeping,   0 stopped,   0 zombie
%Cpu(s):  4.0 us, 95.5 sy,  0.0 ni,  0.2 id,  0.1 wa,  0.0 hi,  0.2 si,  0.0 st
KiB Mem:   8069208 total,  4414640 used,  3654568 free,   475752 buffers
KiB Swap:  9525244 total,        0 used,  9525244 free.  2063192 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                                             
 3343 mysql     20   0  549944  47456  10492 S 171.9  0.6  60:21.11 mysqld                                                                                                                              


Looking at it, it just loops over the io_getevents syscall:


nemi:/tmp# strace -fp 3343
Process 3343 attached with 17 threads
[pid  3414] futex(0x7f08cbf43ba4, FUTEX_WAIT_PRIVATE, 95, NULL <unfinished ...>
[pid  3410] rt_sigtimedwait([HUP QUIT ALRM TERM TSTP], NULL, NULL, 8 <unfinished ...>
[pid  3396] futex(0x7f08cd669a0c, FUTEX_WAIT_PRIVATE, 1, NULL <unfinished ...>
[pid  3395] restart_syscall(<... resuming interrupted call ...> <unfinished ...>
[pid  3393] restart_syscall(<... resuming interrupted call ...> <unfinished ...>
[pid  3375] io_getevents(139675742199808, 1, 256,  <unfinished ...>
[pid  3394] restart_syscall(<... resuming interrupted call ...> <unfinished ...>
[pid  3343] restart_syscall(<... resuming interrupted call ...> <unfinished ...>
[pid  3368] io_getevents(139675744239616, 1, 256,  <unfinished ...>
[pid  3370] io_getevents(139675744198656, 1, 256,  <unfinished ...>
[pid  3372] io_getevents(139675744157696, 1, 256,  <unfinished ...>
[pid  3369] io_getevents(139675744219136, 1, 256,  <unfinished ...>
[pid  3376] io_getevents(139675696115712, 1, 256,  <unfinished ...>
[pid  3377] io_getevents(139675696095232, 1, 256,  <unfinished ...>
[pid  3371] io_getevents(139675744178176, 1, 256,  <unfinished ...>
[pid  3374] io_getevents(139675742220288, 1, 256,  <unfinished ...>
[pid  3373] io_getevents(139675742240768, 1, 256,  <unfinished ...>
[pid  3375] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3368] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3370] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3370] io_getevents(139675744198656, 1, 256,  <unfinished ...>
[pid  3372] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3372] io_getevents(139675744157696, 1, 256,  <unfinished ...>
[pid  3369] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3375] io_getevents(139675742199808, 1, 256,  <unfinished ...>
[pid  3368] io_getevents(139675744239616, 1, 256,  <unfinished ...>
[pid  3376] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3369] io_getevents(139675744219136, 1, 256,  <unfinished ...>
[pid  3376] io_getevents(139675696115712, 1, 256,  <unfinished ...>
[pid  3377] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3377] io_getevents(139675696095232, 1, 256,  <unfinished ...>
[pid  3373] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3371] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3374] <... io_getevents resumed> {}{0, 500000000}) = 0
[pid  3371] io_getevents(139675744178176, 1, 256,  <unfinished ...>
[pid  3374] io_getevents(139675742220288, 1, 256,  <unfinished ...>



I have not tried to repeat this yet, so I don't know if it is
reproducable.  FWIW, it never happened to me with v3.18.  I send this to
you because it looks like you touched this code path between v3.18 and
v3.19-rc1, so I hope you have a clue what's going on here...  Ref:



commit 5f785de588735306ec4d7c875caf9d28481c8b21
Author: Fam Zheng <famz@...hat.com>
Date:   Thu Nov 6 20:44:36 2014 +0800

    aio: Skip timer for io_getevents if timeout=0
    
    In this case, it is basically a polling. Let's not involve timer at all
    because that would hurt performance for application event loops.
    
    In an arbitrary test I've done, io_getevents syscall elapsed time
    reduces from 50000+ nanoseconds to a few hundereds.
    
    Signed-off-by: Fam Zheng <famz@...hat.com>
    Signed-off-by: Benjamin LaHaise <bcrl@...ck.org>

diff --git a/fs/aio.c b/fs/aio.c
index bfab55607a4d..1b7893ecc296 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1253,8 +1253,12 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
         * the ringbuffer empty. So in practice we should be ok, but it's
         * something to be aware of when touching this code.
         */
-       wait_event_interruptible_hrtimeout(ctx->wait,
-                       aio_read_events(ctx, min_nr, nr, event, &ret), until);
+       if (until.tv64 == 0)
+               aio_read_events(ctx, min_nr, nr, event, &ret);
+       else
+               wait_event_interruptible_hrtimeout(ctx->wait,
+                               aio_read_events(ctx, min_nr, nr, event, &ret),
+                               until);
 
        if (!ret && signal_pending(current))
                ret = -EINTR;





Bjørn
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