From: Hugh Dickins <hughd@xxxxxxxxxx> Subject: shmem: shmem_writepage() split unlikely i915 THP 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(). Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008301401390.5954@eggly.anvils Fixes: 2d6692e642e7 ("drm/i915: Start writeback from the shrinker") Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Yang Shi <shy828301@xxxxxxxxx> Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [5.3+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/shmem.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/mm/shmem.c~shmem-shmem_writepage-split-unlikely-i915-thp +++ a/mm/shmem.c @@ -1362,7 +1362,15 @@ static int shmem_writepage(struct page * swp_entry_t swap; pgoff_t index; - VM_BUG_ON_PAGE(PageCompound(page), page); + /* + * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "force", + * then drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages, + * and its shmem_writeback() needs them to be split when swapping. + */ + if (PageTransCompound(page)) + if (split_huge_page(page) < 0) + goto redirty; + BUG_ON(!PageLocked(page)); mapping = page->mapping; index = page->index; _
