Messages in this thread | | | Date | Mon, 9 Nov 2020 11:24:37 +0100 | From | Pavel Machek <> | Subject | 4.19-stable: Re: [PATCH 2/3] drm/i915: Break up error capture compression loops with cond_resched() |
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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 [unhandled content-type:application/pgp-signature] | |