On Sun, 8 Dec 2019 at 16:13, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
>
> As i915_gem_object_unbind() waits on an rcu_barrier() to flush vm
> releases (and destruction of their bound vma), we have to be careful not
> to invoke that barrier from beneath the shrinker:
>
> <4> [430.222671] WARNING: possible circular locking dependency detected
> <4> [430.222673] 5.4.0-rc8-CI-CI_DRM_7508+ #1 Tainted: G U
> <4> [430.222675] ------------------------------------------------------
> <4> [430.222677] gem_pwrite/2317 is trying to acquire lock:
> <4> [430.222678] ffffffff82248218 (rcu_state.barrier_mutex){+.+.}, at: rcu_barrier+0x23/0x190
> <4> [430.222685]
> but task is already holding lock:
> <4> [430.222687] ffffffff82263a40 (fs_reclaim){+.+.}, at: fs_reclaim_acquire.part.117+0x0/0x30
> <4> [430.222691]
> which lock already depends on the new lock.
>
> <4> [430.222693]
> the existing dependency chain (in reverse order) is:
> <4> [430.222695]
> -> #2 (fs_reclaim){+.+.}:
> <4> [430.222698] fs_reclaim_acquire.part.117+0x24/0x30
> <4> [430.222702] kmem_cache_alloc_trace+0x2a/0x2c0
> <4> [430.222705] intel_cpuc_prepare+0x37/0x1a0
> <4> [430.222709] cpuhp_invoke_callback+0x9b/0x9d0
> <4> [430.222712] _cpu_up+0xa2/0x140
> <4> [430.222714] do_cpu_up+0x61/0xa0
> <4> [430.222718] smp_init+0x57/0x96
> <4> [430.222722] kernel_init_freeable+0xac/0x1c7
> <4> [430.222725] kernel_init+0x5/0x100
> <4> [430.222728] ret_from_fork+0x24/0x50
> <4> [430.222729]
> -> #1 (cpu_hotplug_lock.rw_sem){++++}:
> <4> [430.222733] cpus_read_lock+0x34/0xd0
> <4> [430.222734] rcu_barrier+0xaa/0x190
> <4> [430.222736] kernel_init+0x21/0x100
> <4> [430.222737] ret_from_fork+0x24/0x50
> <4> [430.222739]
> -> #0 (rcu_state.barrier_mutex){+.+.}:
> <4> [430.222742] __lock_acquire+0x1328/0x15d0
> <4> [430.222743] lock_acquire+0xa7/0x1c0
> <4> [430.222746] __mutex_lock+0x9a/0x9d0
> <4> [430.222747] rcu_barrier+0x23/0x190
> <4> [430.222850] i915_gem_object_unbind+0x264/0x3d0 [i915]
> <4> [430.222882] i915_gem_shrink+0x297/0x5f0 [i915]
> <4> [430.222912] i915_gem_shrink_all+0x38/0x60 [i915]
> <4> [430.222934] i915_drop_caches_set+0x1f0/0x240 [i915]
> <4> [430.222938] simple_attr_write+0xb0/0xd0
> <4> [430.222941] full_proxy_write+0x51/0x80
> <4> [430.222943] vfs_write+0xb9/0x1d0
> <4> [430.222944] ksys_write+0x9f/0xe0
> <4> [430.222946] do_syscall_64+0x4f/0x210
> <4> [430.222948] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> <4> [430.222950]
> other info that might help us debug this:
>
> <4> [430.222952] Chain exists of:
> rcu_state.barrier_mutex --> cpu_hotplug_lock.rw_sem --> fs_reclaim
>
> <4> [430.222955] Possible unsafe locking scenario:
>
> <4> [430.222957] CPU0 CPU1
> <4> [430.222958] ---- ----
> <4> [430.222960] lock(fs_reclaim);
> <4> [430.222961] lock(cpu_hotplug_lock.rw_sem);
> <4> [430.222963] lock(fs_reclaim);
> <4> [430.222964] lock(rcu_state.barrier_mutex);
> <4> [430.222966]
> *** DEADLOCK ***
>
> <4> [430.222968] 3 locks held by gem_pwrite/2317:
> <4> [430.222969] #0: ffff88849e2d9408 (sb_writers#14){.+.+}, at: vfs_write+0x1a4/0x1d0
> <4> [430.222973] #1: ffff888496976db0 (&attr->mutex){+.+.}, at: simple_attr_write+0x36/0xd0
> <4> [430.222976] #2: ffffffff82263a40 (fs_reclaim){+.+.}, at: fs_reclaim_acquire.part.117+0x0/0x30
> <4> [430.222980]
> stack backtrace:
> <4> [430.222982] CPU: 1 PID: 2317 Comm: gem_pwrite Tainted: G U 5.4.0-rc8-CI-CI_DRM_7508+ #1
> <4> [430.222985] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake U DDR4 SODIMM RVP, BIOS TGLSFWI1.R00.2321.A08.1909162051 09/16/2019
> <4> [430.222989] Call Trace:
> <4> [430.222992] dump_stack+0x71/0x9b
> <4> [430.222995] check_noncircular+0x19b/0x1c0
> <4> [430.222998] ? __lock_acquire+0x1328/0x15d0
> <4> [430.222999] __lock_acquire+0x1328/0x15d0
> <4> [430.223001] ? mark_held_locks+0x49/0x70
> <4> [430.223003] lock_acquire+0xa7/0x1c0
> <4> [430.223005] ? rcu_barrier+0x23/0x190
> <4> [430.223008] __mutex_lock+0x9a/0x9d0
> <4> [430.223009] ? rcu_barrier+0x23/0x190
> <4> [430.223011] ? rcu_barrier+0x23/0x190
> <4> [430.223013] ? find_held_lock+0x2d/0x90
> <4> [430.223045] ? i915_gem_object_unbind+0x24a/0x3d0 [i915]
> <4> [430.223048] ? rcu_barrier+0x23/0x190
> <4> [430.223049] rcu_barrier+0x23/0x190
> <4> [430.223081] i915_gem_object_unbind+0x264/0x3d0 [i915]
> <4> [430.223119] i915_gem_shrink+0x297/0x5f0 [i915]
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
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