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kernel: backport slub prefetch fix from v4.19

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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
This commit is contained in:
Matthias Schiffer 2020-04-25 19:31:12 +02:00 committed by Martin Weinelt
parent 079275ebf2
commit 35e8b53385
1 changed files with 63 additions and 0 deletions
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63
patches/openwrt/0010-kernel-backport-slub-prefetch-fix-from-v4.19.patch Normal file
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@ -0,0 +1,63 @@
From: Matthias Schiffer <mschiffer@universe-factory.net>
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 <mschiffer@universe-factory.net>
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 <vbabka@suse.cz>
+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 <vbabka@suse.cz>
+Acked-by: Kees Cook <keescook@chromium.org>
+Cc: Daniel Micay <danielmicay@gmail.com>
+Cc: Eric Dumazet <edumazet@google.com>
+Cc: Christoph Lameter <cl@linux.com>
+Cc: Pekka Enberg <penberg@kernel.org>
+Cc: David Rientjes <rientjes@google.com>
+Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
+Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+---
+ 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)