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From: Sultan Alsawaf <sultan@kerneltoast.com>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: dri-devel@lists.freedesktop.org, David Airlie <airlied@linux.ie>,
	Greg KH <gregkh@linuxfoundation.org>,
	intel-gfx@lists.freedesktop.org, stable@vger.kernel.org,
	Rodrigo Vivi <rodrigo.vivi@intel.com>
Subject: Re: [PATCH v2] drm/i915: Fix ref->mutex deadlock in i915_active_wait()
Date: Tue, 14 Apr 2020 07:35:18 -0700	[thread overview]
Message-ID: <20200414143518.GA2082@sultan-box.localdomain> (raw)
In-Reply-To: <158685210730.16269.15932754047962572236@build.alporthouse.com>

On Tue, Apr 14, 2020 at 09:15:07AM +0100, Chris Wilson wrote:
> The patch does not fix a deadlock. Greg, this patch is not a backport of
> a bugfix, why is it in stable?
> -Chris

Here's the deadlock this supposedly doesn't fix:
INFO: task kswapd0:178 blocked for more than 122 seconds.
      Tainted: G     U            5.4.28-00014-gd1e04f91d2c5 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kswapd0         D    0   178      2 0x80004000
Call Trace:
 ? __schedule+0x2f3/0x750
 schedule+0x39/0xa0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.isra.0+0x19b/0x500
 ? i915_request_wait+0x25b/0x370
 active_retire+0x26/0x30
 i915_active_wait+0xa3/0x1a0
 i915_vma_unbind+0xe2/0x1c0
 i915_gem_object_unbind+0x111/0x140
 i915_gem_shrink+0x21b/0x530
 i915_gem_shrinker_scan+0xfd/0x120
 do_shrink_slab+0x154/0x2c0
 shrink_slab+0xd0/0x2f0
 shrink_node+0xdf/0x420
 balance_pgdat+0x2e3/0x540
 kswapd+0x200/0x3c0
 ? __wake_up_common_lock+0xc0/0xc0
 kthread+0xfb/0x130
 ? balance_pgdat+0x540/0x540
 ? __kthread_parkme+0x60/0x60
 ret_from_fork+0x1f/0x40
INFO: task kworker/u32:5:222 blocked for more than 122 seconds.
      Tainted: G     U            5.4.28-00014-gd1e04f91d2c5 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u32:5   D    0   222      2 0x80004000
Workqueue: i915 idle_work_handler
Call Trace:
 ? __schedule+0x2f3/0x750
 schedule+0x39/0xa0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.isra.0+0x19b/0x500
 idle_work_handler+0x34/0x120
 process_one_work+0x1ea/0x3a0
 worker_thread+0x4d/0x3f0
 kthread+0xfb/0x130
 ? process_one_work+0x3a0/0x3a0
 ? __kthread_parkme+0x60/0x60
 ret_from_fork+0x1f/0x40
INFO: task mpv:1535 blocked for more than 122 seconds.
      Tainted: G     U            5.4.28-00014-gd1e04f91d2c5 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
mpv             D    0  1535      1 0x00000000
Call Trace:
 ? __schedule+0x2f3/0x750
 schedule+0x39/0xa0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.isra.0+0x19b/0x500
 __i915_gem_free_objects+0x68/0x190
 i915_gem_create_ioctl+0x18/0x30
 ? i915_gem_dumb_create+0xa0/0xa0
 drm_ioctl_kernel+0xb2/0x100
 drm_ioctl+0x209/0x360
 ? i915_gem_dumb_create+0xa0/0xa0
 do_vfs_ioctl+0x43f/0x6c0
 ksys_ioctl+0x5e/0x90
 __x64_sys_ioctl+0x16/0x20
 do_syscall_64+0x4e/0x140
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fb49f1b32eb
Code: Bad RIP value.
RSP: 002b:00007ffef9eb0948 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffef9eb09c0 RCX: 00007fb49f1b32eb
RDX: 00007ffef9eb09c0 RSI: 00000000c010645b RDI: 0000000000000008
RBP: 00000000c010645b R08: 000055fdb80c1370 R09: 000055fdb80c14e0
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb4781e56b0
R13: 0000000000000008 R14: 00007fb4781e5560 R15: 00007fb4781e56b0
INFO: task kswapd0:178 blocked for more than 245 seconds.
      Tainted: G     U            5.4.28-00014-gd1e04f91d2c5 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kswapd0         D    0   178      2 0x80004000
Call Trace:
 ? __schedule+0x2f3/0x750
 schedule+0x39/0xa0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.isra.0+0x19b/0x500
 ? i915_request_wait+0x25b/0x370
 active_retire+0x26/0x30
 i915_active_wait+0xa3/0x1a0
 i915_vma_unbind+0xe2/0x1c0
 i915_gem_object_unbind+0x111/0x140
 i915_gem_shrink+0x21b/0x530
 i915_gem_shrinker_scan+0xfd/0x120
 do_shrink_slab+0x154/0x2c0
 shrink_slab+0xd0/0x2f0
 shrink_node+0xdf/0x420
 balance_pgdat+0x2e3/0x540
 kswapd+0x200/0x3c0
 ? __wake_up_common_lock+0xc0/0xc0
 kthread+0xfb/0x130
 ? balance_pgdat+0x540/0x540
 ? __kthread_parkme+0x60/0x60
 ret_from_fork+0x1f/0x40
INFO: task kworker/u32:5:222 blocked for more than 245 seconds.
      Tainted: G     U            5.4.28-00014-gd1e04f91d2c5 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u32:5   D    0   222      2 0x80004000
Workqueue: i915 idle_work_handler
Call Trace:
 ? __schedule+0x2f3/0x750
 schedule+0x39/0xa0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.isra.0+0x19b/0x500
 idle_work_handler+0x34/0x120
 process_one_work+0x1ea/0x3a0
 worker_thread+0x4d/0x3f0
 kthread+0xfb/0x130
 ? process_one_work+0x3a0/0x3a0
 ? __kthread_parkme+0x60/0x60
 ret_from_fork+0x1f/0x40
INFO: task mpv:1535 blocked for more than 245 seconds.
      Tainted: G     U            5.4.28-00014-gd1e04f91d2c5 #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
mpv             D    0  1535      1 0x00000000
Call Trace:
 ? __schedule+0x2f3/0x750
 schedule+0x39/0xa0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.isra.0+0x19b/0x500
 __i915_gem_free_objects+0x68/0x190
 i915_gem_create_ioctl+0x18/0x30
 ? i915_gem_dumb_create+0xa0/0xa0
 drm_ioctl_kernel+0xb2/0x100
 drm_ioctl+0x209/0x360
 ? i915_gem_dumb_create+0xa0/0xa0
 do_vfs_ioctl+0x43f/0x6c0
 ksys_ioctl+0x5e/0x90
 __x64_sys_ioctl+0x16/0x20
 do_syscall_64+0x4e/0x140
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fb49f1b32eb
Code: Bad RIP value.
RSP: 002b:00007ffef9eb0948 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffef9eb09c0 RCX: 00007fb49f1b32eb
RDX: 00007ffef9eb09c0 RSI: 00000000c010645b RDI: 0000000000000008
RBP: 00000000c010645b R08: 000055fdb80c1370 R09: 000055fdb80c14e0
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb4781e56b0
R13: 0000000000000008 R14: 00007fb4781e5560 R15: 00007fb4781e56b0

Dead inside the shrinker, and very easy to reproduce.

Sultan
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  parent reply	other threads:[~2020-04-15  7:18 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200407062622.6443-1-sultan@kerneltoast.com>
2020-04-07  6:52 ` [PATCH 0/1] drm/i915: Fix a deadlock that only affects 5.4 Greg KH
     [not found]   ` <20200407071809.3148-1-sultan@kerneltoast.com>
2020-04-10  9:08     ` [PATCH v2] drm/i915: Fix ref->mutex deadlock in i915_active_wait() Greg KH
2020-04-10 14:15       ` Sultan Alsawaf
2020-04-10 14:17       ` Sultan Alsawaf
2020-04-11 11:39         ` Greg KH
2020-04-14  8:15           ` Chris Wilson
2020-04-14  8:23             ` Greg KH
2020-04-20  9:02               ` Joonas Lahtinen
2020-04-20 15:42                 ` Sultan Alsawaf
2020-04-21  8:04                   ` Joonas Lahtinen
2020-04-21 16:38                     ` Sultan Alsawaf
2020-04-21 20:55                       ` Jason A. Donenfeld
2020-04-14 14:35             ` Sultan Alsawaf [this message]
2020-04-10 11:46     ` Patch "drm/i915: Fix ref->mutex deadlock in i915_active_wait()" has been added to the 5.4-stable tree gregkh
     [not found] ` <20200407062622.6443-2-sultan@kerneltoast.com>
2020-04-14  8:13   ` [PATCH 1/1] drm/i915: Fix ref->mutex deadlock in i915_active_wait() Chris Wilson
2020-04-14 14:52     ` Sultan Alsawaf

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