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From: Pavel Machek <pavel@ucw.cz>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	kernel list <linux-kernel@vger.kernel.org>
Cc: intel-gfx@lists.freedesktop.org, stable@vger.kernel.org
Subject: [Intel-gfx] 4.19-stable: Re: [PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched()
Date: Mon, 9 Nov 2020 11:24:37 +0100	[thread overview]
Message-ID: <20201109102437.GA15835@amd> (raw)
In-Reply-To: <20200916090059.3189-2-chris@chris-wilson.co.uk>


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Hi!

> As the error capture will compress user buffers as directed to by the
> user, it can take an arbitrary amount of time and space. Break up the
> compression loops with a call to cond_resched(), that will allow other
> processes to schedule (avoiding the soft lockups) and also serve as a
> warning should we try to make this loop atomic in the future.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: stable@vger.kernel.org
> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

This was queued for 4.19-stable, but is very likely wrong.

> @@ -397,6 +399,7 @@ static int compress_page(struct i915_vma_compress *c,
>  	if (!(wc && i915_memcpy_from_wc(ptr, src, PAGE_SIZE)))
>  		memcpy(ptr, src, PAGE_SIZE);
>  	dst->pages[dst->page_count++] = ptr;
> +	cond_resched();
>  
>  	return 0;
>  }

4.19 compress_page begins with

static int compress_page(struct compress *c,
...
        page = __get_free_page(GFP_ATOMIC | __GFP_NOWARN);

and likely may not sleep. That changed with commit
a42f45a2a85998453078, but that one is not present in 4.19..

I believe we don't need this in stable: dumping of error file will not
take so long to trigger softlockup detectors... and if userland access
blocked, we would be able to reschedule, anyway.

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

WARNING: multiple messages have this Message-ID (diff)
From: Pavel Machek <pavel@ucw.cz>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	kernel list <linux-kernel@vger.kernel.org>
Cc: intel-gfx@lists.freedesktop.org,
	Mika Kuoppala <mika.kuoppala@linux.intel.com>,
	stable@vger.kernel.org
Subject: 4.19-stable: Re: [PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched()
Date: Mon, 9 Nov 2020 11:24:37 +0100	[thread overview]
Message-ID: <20201109102437.GA15835@amd> (raw)
In-Reply-To: <20200916090059.3189-2-chris@chris-wilson.co.uk>

[-- Attachment #1: Type: text/plain, Size: 1433 bytes --]

Hi!

> As the error capture will compress user buffers as directed to by the
> user, it can take an arbitrary amount of time and space. Break up the
> compression loops with a call to cond_resched(), that will allow other
> processes to schedule (avoiding the soft lockups) and also serve as a
> warning should we try to make this loop atomic in the future.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: stable@vger.kernel.org
> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

This was queued for 4.19-stable, but is very likely wrong.

> @@ -397,6 +399,7 @@ static int compress_page(struct i915_vma_compress *c,
>  	if (!(wc && i915_memcpy_from_wc(ptr, src, PAGE_SIZE)))
>  		memcpy(ptr, src, PAGE_SIZE);
>  	dst->pages[dst->page_count++] = ptr;
> +	cond_resched();
>  
>  	return 0;
>  }

4.19 compress_page begins with

static int compress_page(struct compress *c,
...
        page = __get_free_page(GFP_ATOMIC | __GFP_NOWARN);

and likely may not sleep. That changed with commit
a42f45a2a85998453078, but that one is not present in 4.19..

I believe we don't need this in stable: dumping of error file will not
take so long to trigger softlockup detectors... and if userland access
blocked, we would be able to reschedule, anyway.

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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  parent reply	other threads:[~2020-11-09 10:33 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-16  9:00 [Intel-gfx] [PATCH 1/3] drm/i915/gt: Show engine properties in the pretty printer Chris Wilson
2020-09-16  9:00 ` [Intel-gfx] [PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched() Chris Wilson
2020-09-16  9:00   ` Chris Wilson
2020-09-21 12:54   ` [Intel-gfx] " Sasha Levin
2020-09-21 12:54     ` Sasha Levin
2020-11-09 10:24   ` Pavel Machek [this message]
2020-11-09 10:24     ` 4.19-stable: " Pavel Machek
2020-09-16  9:00 ` [Intel-gfx] [PATCH 3/3] drm/i915: Reduce GPU error capture mutex hold time Chris Wilson
2020-09-16 17:51   ` Matthew Auld
2020-09-16 12:34 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for series starting with [1/3] drm/i915/gt: Show engine properties in the pretty printer Patchwork
2020-09-16 12:34 ` [Intel-gfx] ✗ Fi.CI.SPARSE: " Patchwork
2020-09-16 12:59 ` [Intel-gfx] ✓ Fi.CI.BAT: success " Patchwork
2020-09-16 16:57 ` [Intel-gfx] ✓ Fi.CI.IGT: " Patchwork

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