linux-kernel - Re: task_ctx_sched_out WARN

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Date:	Fri, 10 Jan 2014 10:05:49 -0500
From:	Dave Jones <davej@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: task_ctx_sched_out WARN_ON triggered.

On Fri, Jan 10, 2014 at 11:48:37AM +0100, Peter Zijlstra wrote:
 > On Thu, Jan 09, 2014 at 10:47:07AM -0500, Dave Jones wrote:
 > > This is my fuzz tester, but this looks to be part of normal operation,
 > > not actually fuzzing a syscall. This looks to be the bit that
 > > sets the task_comm name in the child process to 'trinity-cN'.  Which appears to have
 > > succeeded judging by the Comm:, but the follow-on perf stuff seems to
 > > be screwed up.
 > > 
 > > WARNING: CPU: 1 PID: 13500 at kernel/events/core.c:2379 task_ctx_sched_out+0x6b/0x80()
 > > Modules linked in: 8021q garp stp snd_seq_dummy tun fuse rfcomm hidp sctp bnep can_raw scsi_transport_iscsi nfc caif_socket caif af_802154 phonet af_rxrpc bluetooth can_bcm can llc2 pppoe pppox ppp_generic slhc nfnetlink irda ipt_ULOG crc_ccitt rds af_key rose x25 atm netrom appletalk ipx p8023 psnap p8022 llc ax25 cfg80211 rfkill coretemp hwmon x86_pkg_temp_thermal kvm_intel kvm xfs snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep libcrc32c snd_seq e1000e snd_seq_device crct10dif_pclmul crc32c_intel ghash_clmulni_intel snd_pcm ptp snd_page_alloc shpchp snd_timer snd microcode serio_raw soundcore usb_debug pcspkr pps_core
 > > CPU: 1 PID: 13500 Comm: trinity-c5 Not tainted 3.13.0-rc7+ #14 
 > >  ffffffff81a240ac ffff88002e0c7df8 ffffffff816de2ee 0000000000000000
 > >  ffff88002e0c7e30 ffffffff81052ddd ffff88024d0975f8 ffff880214d7bb10
 > >  0000000000000282 ffff88015b3b24c0 ffff880214d7bb10 ffff88002e0c7e40
 > > Call Trace:
 > >  [<ffffffff816de2ee>] dump_stack+0x4e/0x7a
 > >  [<ffffffff81052ddd>] warn_slowpath_common+0x7d/0xa0
 > >  [<ffffffff81052eba>] warn_slowpath_null+0x1a/0x20
 > >  [<ffffffff81128d5b>] task_ctx_sched_out+0x6b/0x80
 > >  [<ffffffff8112ba78>] perf_event_comm+0x108/0x260
 > >  [<ffffffff8112b970>] ? perf_event_fork+0x20/0x20
 > >  [<ffffffff811a3815>] ? set_task_comm+0x25/0xc0
 > >  [<ffffffff811a383f>] set_task_comm+0x4f/0xc0
 > >  [<ffffffff8106b039>] SyS_prctl+0x229/0x3d0
 > >  [<ffffffff816f0b24>] tracesys+0xdd/0xe2
 > > ---[ end trace d6e98e080907af47 ]---
 > > 
 > > 
 > > 2379         if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
 > > 2380                 return;
 > 
 > Hmm, you wouldn't happen to have the perf_event_attr for all active
 > events, would you?

I don't. I'll start adding some code soon to log the contents of the
structures being passed to syscalls as well as just the address.

I've hit this bug twice in the last 24 hrs though, which is promising.

	Dave

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