From 4d5c0d195850d1502a837b0f46f482e4d26e6f95 Mon Sep 17 00:00:00 2001 From: Matthias Schiffer Date: Sat, 25 Apr 2020 19:31:12 +0200 Subject: [PATCH] kernel: backport slub prefetch fix from v4.19 This patch fixes a regression introduced in kernel v4.14. While the commit message only mentions a performance penalty, the issue is suspected to be the cause of spurious data bus errors on MIPS CPUs (ar71xx target). Fixes: #1982 (cherry picked from commit 35e8b533852dcedb25bdd017d0269309be933fc9) --- ...ackport-slub-prefetch-fix-from-v4.19.patch | 63 +++++++++++++++++++ 1 file changed, 63 insertions(+) create mode 100644 patches/openwrt/0010-kernel-backport-slub-prefetch-fix-from-v4.19.patch diff --git a/patches/openwrt/0010-kernel-backport-slub-prefetch-fix-from-v4.19.patch b/patches/openwrt/0010-kernel-backport-slub-prefetch-fix-from-v4.19.patch new file mode 100644 index 00000000..cc82990c --- /dev/null +++ b/patches/openwrt/0010-kernel-backport-slub-prefetch-fix-from-v4.19.patch @@ -0,0 +1,63 @@ +From: Matthias Schiffer +Date: Sat, 25 Apr 2020 19:27:34 +0200 +Subject: kernel: backport slub prefetch fix from v4.19 + +This patch fixes a regression introduced in kernel v4.14. While the +commit message only mentions a performance penalty, the issue is +suspected to be the cause of spurious data bus errors on MIPS CPUs +(ar71xx target). + +Signed-off-by: Matthias Schiffer + +diff --git a/target/linux/generic/backport-4.14/190-v4.19-mm-slub-restore-the-original-intention-of-prefetch_f.patch b/target/linux/generic/backport-4.14/190-v4.19-mm-slub-restore-the-original-intention-of-prefetch_f.patch +new file mode 100644 +index 0000000000000000000000000000000000000000..06bea3e8fd36b3d9f1e9f14c6928aebc315db19c +--- /dev/null ++++ b/target/linux/generic/backport-4.14/190-v4.19-mm-slub-restore-the-original-intention-of-prefetch_f.patch +@@ -0,0 +1,46 @@ ++From 0882ff9190e3bc51e2d78c3aadd7c690eeaa91d5 Mon Sep 17 00:00:00 2001 ++Message-Id: <0882ff9190e3bc51e2d78c3aadd7c690eeaa91d5.1587834219.git.mschiffer@universe-factory.net> ++From: Vlastimil Babka ++Date: Fri, 17 Aug 2018 15:44:44 -0700 ++Subject: [PATCH] mm, slub: restore the original intention of ++ prefetch_freepointer() ++ ++In SLUB, prefetch_freepointer() is used when allocating an object from ++cache's freelist, to make sure the next object in the list is cache-hot, ++since it's probable it will be allocated soon. ++ ++Commit 2482ddec670f ("mm: add SLUB free list pointer obfuscation") has ++unintentionally changed the prefetch in a way where the prefetch is ++turned to a real fetch, and only the next->next pointer is prefetched. ++In case there is not a stream of allocations that would benefit from ++prefetching, the extra real fetch might add a useless cache miss to the ++allocation. Restore the previous behavior. ++ ++Link: http://lkml.kernel.org/r/20180809085245.22448-1-vbabka@suse.cz ++Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation") ++Signed-off-by: Vlastimil Babka ++Acked-by: Kees Cook ++Cc: Daniel Micay ++Cc: Eric Dumazet ++Cc: Christoph Lameter ++Cc: Pekka Enberg ++Cc: David Rientjes ++Cc: Joonsoo Kim ++Signed-off-by: Andrew Morton ++Signed-off-by: Linus Torvalds ++--- ++ mm/slub.c | 3 +-- ++ 1 file changed, 1 insertion(+), 2 deletions(-) ++ ++--- a/mm/slub.c +++++ b/mm/slub.c ++@@ -269,8 +269,7 @@ static inline void *get_freepointer(stru ++ ++ static void prefetch_freepointer(const struct kmem_cache *s, void *object) ++ { ++- if (object) ++- prefetch(freelist_dereference(s, object + s->offset)); +++ prefetch(object + s->offset); ++ } ++ ++ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)