Re: [PATCH 3/5] shmem: shmem_writepage() split unlikely i915 THP

[Shakeel Butt]

On Sun, Aug 30, 2020 at 2:04 PM Hugh Dickins <hughd@xxxxxxxxxx> wrote:
>
> drivers/gpu/drm/i915/gem/i915_gem_shmem.c contains a shmem_writeback()
> which calls shmem_writepage() from a shrinker: that usually works well
> enough; but if /sys/kernel/mm/transparent_hugepage/shmem_enabled has
> been set to "force" (documented as "Force the huge option on for all -
> very useful for testing"), shmem_writepage() is surprised to be called
> with a huge page, and crashes on the VM_BUG_ON_PAGE(PageCompound) (I
> did not find out where the crash happens when CONFIG_DEBUG_VM is off).
>
> LRU page reclaim always splits the shmem huge page first: I'd prefer not
> to demand that of i915, so check and split compound in shmem_writepage().
>
> Fixes: 2d6692e642e7 ("drm/i915: Start writeback from the shrinker")
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.3+

Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>