From: Hugh Dickins <hughd@google.com> To: Andrew Morton <akpm@linux-foundation.org> Cc: Alex Shi <alex.shi@linux.alibaba.com>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.com>, Mike Kravetz <mike.kravetz@oracle.com>, Shakeel Butt <shakeelb@google.com>, Matthew Wilcox <willy@infradead.org>, Qian Cai <cai@lca.pw>, Chris Wilson <chris@chris-wilson.co.uk>, Kuo-Hsin Yang <vovoy@chromium.org>, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 3/5] shmem: shmem_writepage() split unlikely i915 THP Date: Sun, 30 Aug 2020 14:04:53 -0700 (PDT) Message-ID: <alpine.LSU.2.11.2008301401390.5954@eggly.anvils> (raw) 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@google.com> Cc: stable@vger.kernel.org # v5.3+ --- I've marked this for stable just for the info, but the number of users affected is very probably 1, so please feel free to delete that marking. mm/shmem.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- 5.9-rc2/mm/shmem.c 2020-08-16 17:32:50.693507198 -0700 +++ linux/mm/shmem.c 2020-08-28 17:35:08.326024349 -0700 @@ -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;
next reply index Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-08-30 21:04 Hugh Dickins [this message] 2020-08-31 14:41 ` Shakeel Butt 2020-09-01 15:39 ` Yang Shi 2020-09-01 17:39 ` Hugh Dickins 2020-09-01 18:50 ` Yang Shi
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