[Intel-gfx] [PATCH] drm/i915: Kill context before taking ctx->mutex

[Tvrtko Ursulin]

On 24/06/2020 12:05, Maarten Lankhorst wrote:
> Killing context before taking ctx->mutex fixes a hang in
> gem_ctx_persistence.close-replace-race, where lut_close
> takes obj->resv.lock which is already held by execbuf,
> causing a stalling indefinitely.

If this is the consequence of inverting the locking order I think you 
need to move the fix earlier in the series, to precede the patch which 
creates the inversion. Otherwise AFAICT the re-order of kill_context vs 
lut_close seems fine.

Regards,

Tvrtko

> [ 1904.342847] 2 locks held by gem_ctx_persist/11520:
> [ 1904.342849]  #0: ffff8882188e4968 (&ctx->mutex){+.+.}-{3:3}, at: context_close+0xe6/0x850 [i915]
> [ 1904.342941]  #1: ffff88821c58a5a8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: lut_close+0x2c2/0xba0 [i915]
> [ 1904.343033] 3 locks held by gem_ctx_persist/11521:
> [ 1904.343035]  #0: ffffc900008ff938 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_gem_do_execbuffer+0x103d/0x54c0 [i915]
> [ 1904.343157]  #1: ffff88821c58a5a8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: eb_validate_vmas+0x602/0x2010 [i915]
> [ 1904.343267]  #2: ffff88820afd9200 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x335/0x2300 [i915]
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_context.c | 22 ++++++++++-----------
>   1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index a3519d5ee5a3..6d25c9c2be1a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -623,6 +623,17 @@ static void context_close(struct i915_gem_context *ctx)
>   	i915_gem_context_set_closed(ctx);
>   	mutex_unlock(&ctx->engines_mutex);
>   
> +	/*
> +	 * If the user has disabled hangchecking, we can not be sure that
> +	 * the batches will ever complete after the context is closed,
> +	 * keeping the context and all resources pinned forever. So in this
> +	 * case we opt to forcibly kill off all remaining requests on
> +	 * context close.
> +	 */
> +	if (!i915_gem_context_is_persistent(ctx) ||
> +	    !ctx->i915->params.enable_hangcheck)
> +		kill_context(ctx);
> +
>   	mutex_lock(&ctx->mutex);
>   
>   	set_closed_name(ctx);
> @@ -642,17 +653,6 @@ static void context_close(struct i915_gem_context *ctx)
>   
>   	mutex_unlock(&ctx->mutex);
>   
> -	/*
> -	 * If the user has disabled hangchecking, we can not be sure that
> -	 * the batches will ever complete after the context is closed,
> -	 * keeping the context and all resources pinned forever. So in this
> -	 * case we opt to forcibly kill off all remaining requests on
> -	 * context close.
> -	 */
> -	if (!i915_gem_context_is_persistent(ctx) ||
> -	    !ctx->i915->params.enable_hangcheck)
> -		kill_context(ctx);
> -
>   	i915_gem_context_put(ctx);
>   }
>   
> 
> base-commit: 64cab0b9f9bfeb14d3ec2452d76b56915cdeb09f
> prerequisite-patch-id: e6315738715ac4ffccaeb4c4bf5a94651fb8da1d
> prerequisite-patch-id: 7944bb01d1ec7530513eabddb9198275653cc451
> prerequisite-patch-id: 052eda3b40906f0fbc16b4cc33dbcdce35e05441
> prerequisite-patch-id: 35ff18a74e8bf9bfb0a517f69a98d0ec88bd3b51
> prerequisite-patch-id: 7a34e785e951b1d3f4c0e20430c8111a15ddbe92
> prerequisite-patch-id: 9b7faf3172e9f218a2589fcc96930af9ab05e70b
> prerequisite-patch-id: 3ce7c5b4508018631673e62d8725f866988bd08d
> prerequisite-patch-id: 5fd46caff26e53f9cb6df5f8490838b6ac15e015
> prerequisite-patch-id: 41782208b1bc32e448ce29313112030c74bd8421
> prerequisite-patch-id: b6c4d99cb554c0c2268cde5c43e878a48e005e45
> prerequisite-patch-id: 418fdb031a232bba4056171917ee42e997991902
> prerequisite-patch-id: ff5bf0dcdb9191761392b0707481aaf99396dbec
> prerequisite-patch-id: c3dbcef2f1a68f88ae99acbd01ee56847fb3e2da
> prerequisite-patch-id: 18c373676c9bbeb1c11fb2ba5bf4ad728cfea75d
> prerequisite-patch-id: 5b9d8e4535096365d365fdd1ec00f844a4135208
> prerequisite-patch-id: 63bac64548acd514c4a0cb5acb896c8217fb8201
> prerequisite-patch-id: e93b855dd97b24799c59f059cc548f46807ab207
> prerequisite-patch-id: 3d7dc6ecbc2279fb48f0972a911fbffd8d899faa
> prerequisite-patch-id: f1d9e0b7165f80efe984dd0231d1dbd2a9a79950
> prerequisite-patch-id: ed1a168ac98b81b8066f68a0738cfc44a79e8ef1
> prerequisite-patch-id: f813cb8d4c2fe2c1d94b66c3f3fbb787ac241628
> prerequisite-patch-id: 0f0f90eaa4a2e299adddfe1c7134af3810a8e9e2
> prerequisite-patch-id: cb7ffeccd6429fc79aebffb84f62af5e78252461
> prerequisite-patch-id: 78905449b46ad574757a7fb91f58847ea20e09cd
> prerequisite-patch-id: 6d937a49f3c8cd380121f72610072aaaf8c274b1
> prerequisite-patch-id: 0c8d2dee1592395780258488be0350755e7ffd7d
>