[PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched()

[PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched()

[Chris Wilson]

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>
---
 drivers/gpu/drm/i915/i915_gpu_error.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 3e6cbb0d1150..a635ec8d0b94 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -311,6 +311,8 @@ static int compress_page(struct i915_vma_compress *c,
 
 		if (zlib_deflate(zstream, Z_NO_FLUSH) != Z_OK)
 			return -EIO;
+
+		cond_resched();
 	} while (zstream->avail_in);
 
 	/* Fallback to uncompressed if we increase size? */
@@ -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;
 }
-- 
2.20.1

Re: [PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched()

[Sasha Levin]

Hi

[This is an automated email]

This commit has been processed because it contains a -stable tag.
The stable tag indicates that it's relevant for the following trees: all

The bot has tested the following trees: v5.8.10, v5.4.66, v4.19.146, v4.14.198, v4.9.236, v4.4.236.

v5.8.10: Build OK!
v5.4.66: Build OK!
v4.19.146: Build OK!
v4.14.198: Build OK!
v4.9.236: Failed to apply! Possible dependencies:
    0a97015d45ee ("drm/i915: Compress GPU objects in error state")
    83bc0f5b432f ("drm/i915: Handle incomplete Z_FINISH for compressed error states")
    95374d759ac7 ("drm/i915: Always use the GTT for error capture")
    98a2f411671f ("drm/i915: Allow disabling error capture")
    9f267eb8d2ea ("drm/i915: Stop the machine whilst capturing the GPU crash dump")
    d636951ec01b ("drm/i915: Cleanup instdone collection")
    fc4c79c37e82 ("drm/i915: Consolidate error object printing")

v4.4.236: Failed to apply! Possible dependencies:
    0a97015d45ee ("drm/i915: Compress GPU objects in error state")
    0bc40be85f33 ("drm/i915: Rename intel_engine_cs function parameters")
    688e6c725816 ("drm/i915: Slaughter the thundering i915_wait_request herd")
    755412e29c77 ("drm/i915: Add an optional selection from i915 of CONFIG_MMU_NOTIFIER")
    98a2f411671f ("drm/i915: Allow disabling error capture")
    ca82580c9cea ("drm/i915: Do not call API requiring struct_mutex where it is not available")
    cbdc12a9fc9d ("drm/i915: make A0 wa's applied to A1")
    e87a005d90c3 ("drm/i915: add helpers for platform specific revision id range checks")
    ef712bb4b700 ("drm/i915: remove parens around revision ids")
    fffda3f4fb49 ("drm/i915/bxt: add revision id for A1 stepping and use it")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?

-- 
Thanks
Sasha

4.19-stable: Re: [PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched()

[Pavel Machek]

[-- 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

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 181 bytes --]