Re: [PATCH] hrtimer:__run_hrtimer races with enqueue_hrtimer

[Yanmin Zhang <yanmin_zhang@linux.intel.com>]

On Fri, 2012-10-26 at 10:51 +0800, he, bo wrote:
> From: Yanmin Zhang <yanmin.zhang@intel.com>
> 
> We hit a kernel panic at __run_hrtimer=>BUG_ON(timer->state != HRTIMER_STATE_CALLBACK).
> <2>[   10.226053, 3] kernel BUG at /home/android/xiaobing/ymz/r4/hardware/intel/linux-2.6/kernel/hrtimer.c:1228!
> <0>[   10.235682, 3] invalid opcode: 0000 [#1] PREEMPT SMP
> <4>[   10.240716, 3] Modules linked in: wl12xx_sdio wl12xx mac80211 cfg80211 compat btwilink rmi4(C) fmdrv_chr st_drv matrix(C)
> <4>[   10.251651, 3]
> <4>[   10.253391, 3] Pid: 68, comm: kworker/3:4 Tainted: G        WC  3.0.34-140430-g2af538d #45 Intel Corporation CloverTrail/FFRD
> <4>[   10.264674, 3] EIP: 0060:[<c126c7ed>] EFLAGS: 00010002 CPU: 3
> <4>[   10.270411, 3] EIP is at __run_hrtimer+0xbd/0x240
> <4>[   10.275091, 3] EAX: 00000001 EBX: f67fb6b8 ECX: f57b4000 EDX: 00007301
> <4>[   10.281602, 3] ESI: c1d614c0 EDI: f67fb680 EBP: f57b5dd8 ESP: f57b5da8
> <4>[   10.288113, 3]  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
> <0>[   10.293754, 3] Process kworker/3:4 (pid: 68, ti=f57b4000 task=f57aa730 task.ti=f57b4000)
> <0>[   10.301827, 3] Stack:
> <4>[   10.304083, 3]  00000000 c1afef40 f57b5dd8 c167a6e0 f67fb680 20b366e3 f67fb6b8 f57b5e14
> <4>[   10.312069, 3]  00000001 f67fb6b8 00000001 f67fb680 f57b5e28 c126d1e5 f57b5e08 c126f325
> <4>[   10.320055, 3]  00000000 86b9868d 00000001 86b9868d 00000001 00000003 ffffffff 7fffffff
> <0>[   10.328041, 3] Call Trace:
> <4>[   10.330742, 3]  [<c167a6e0>] ? gburst_thread_stop.isra.25+0x40/0x40
> <4>[   10.336988, 3]  [<c126d1e5>] hrtimer_interrupt+0xd5/0x250
> <4>[   10.342368, 3]  [<c126f325>] ? sched_clock_cpu+0xe5/0x150
> <4>[   10.347753, 3]  [<c1871d44>] smp_apic_timer_interrupt+0x54/0x88
> <4>[   10.353654, 3]  [<c1496558>] ? trace_hardirqs_off_thunk+0xc/0x14
> <4>[   10.359643, 3]  [<c186be9f>] apic_timer_interrupt+0x2f/0x34
> <4>[   10.365199, 3]  [<c186e60f>] ? sub_preempt_count+0x1f/0x50
> <4>[   10.370669, 3]  [<c149558a>] delay_tsc+0x3a/0xc0
> <6>[   10.371589, 0] android_work: did not send uevent (0 0   (null))
> <4>[   10.381171, 3]  [<c14954e3>] __const_udelay+0x23/0x30
> <4>[   10.386207, 3]  [<c16d043a>] mdfld_dsi_send_dcs+0x12a/0x5d0
> <4>[   10.391760, 3]  [<c186b6c6>] ? _raw_spin_unlock_irqrestore+0x26/0x50
> <4>[   10.398101, 3]  [<c16af431>] ? ospm_power_using_hw_begin+0xa1/0x350
> <4>[   10.399053, 3]  [<c186a49f>] ? __mutex_lock_slowpath+0x1ff/0x2f0
> <4>[   10.399069, 3]  [<c16bd59e>] mdfld_dbi_update_panel+0x21e/0x2d0
> <4>[   10.399085, 3]  [<c16b1ae1>] mdfld_te_handler_work+0x71/0x80
> <4>[   10.399099, 3]  [<c12642be>] process_one_work+0xfe/0x3f0
> <4>[   10.399114, 3]  [<c16b1a70>] ? mdfld_async_flip_te_handler+0xf0/0xf0
> 
> Basically, __run_hrtimer has a race with enqueue_hrtimer. When __run_hrtimer calls
> the timer callback fn, another thread might call enqueue_hrtimer or hrtimer_start
> to requeue it, and the timer->state is equal to HRTIMER_STATE_CALLBACK|HRTIMER_STATE_ENQUEUED,
> which causes the BUG_ON(timer->state != HRTIMER_STATE_CALLBACK) checking fails.
> 
> The patch fixes it by checking only bit HRTIMER_STATE_CALLBACK.
The patch has an issue that enqueue_hrtimer doesn't check if the timer is queued.
I will send a new patch.