4d5c0d1958
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 35e8b53385)
64 lines
2.8 KiB
Diff
64 lines
2.8 KiB
Diff
From: Matthias Schiffer <mschiffer@universe-factory.net>
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Date: Sat, 25 Apr 2020 19:27:34 +0200
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Subject: kernel: backport slub prefetch fix from v4.19
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This patch fixes a regression introduced in kernel v4.14. While the
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commit message only mentions a performance penalty, the issue is
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suspected to be the cause of spurious data bus errors on MIPS CPUs
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(ar71xx target).
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Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
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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
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new file mode 100644
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index 0000000000000000000000000000000000000000..06bea3e8fd36b3d9f1e9f14c6928aebc315db19c
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--- /dev/null
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+++ b/target/linux/generic/backport-4.14/190-v4.19-mm-slub-restore-the-original-intention-of-prefetch_f.patch
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@@ -0,0 +1,46 @@
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+From 0882ff9190e3bc51e2d78c3aadd7c690eeaa91d5 Mon Sep 17 00:00:00 2001
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+Message-Id: <0882ff9190e3bc51e2d78c3aadd7c690eeaa91d5.1587834219.git.mschiffer@universe-factory.net>
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+From: Vlastimil Babka <vbabka@suse.cz>
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+Date: Fri, 17 Aug 2018 15:44:44 -0700
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+Subject: [PATCH] mm, slub: restore the original intention of
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+ prefetch_freepointer()
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+
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+In SLUB, prefetch_freepointer() is used when allocating an object from
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+cache's freelist, to make sure the next object in the list is cache-hot,
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+since it's probable it will be allocated soon.
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+
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+Commit 2482ddec670f ("mm: add SLUB free list pointer obfuscation") has
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+unintentionally changed the prefetch in a way where the prefetch is
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+turned to a real fetch, and only the next->next pointer is prefetched.
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+In case there is not a stream of allocations that would benefit from
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+prefetching, the extra real fetch might add a useless cache miss to the
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+allocation. Restore the previous behavior.
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+
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+Link: http://lkml.kernel.org/r/20180809085245.22448-1-vbabka@suse.cz
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+Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation")
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+Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
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+Acked-by: Kees Cook <keescook@chromium.org>
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+Cc: Daniel Micay <danielmicay@gmail.com>
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+Cc: Eric Dumazet <edumazet@google.com>
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+Cc: Christoph Lameter <cl@linux.com>
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+Cc: Pekka Enberg <penberg@kernel.org>
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+Cc: David Rientjes <rientjes@google.com>
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+Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
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+Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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+---
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+ mm/slub.c | 3 +--
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+ 1 file changed, 1 insertion(+), 2 deletions(-)
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+
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+--- a/mm/slub.c
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++++ b/mm/slub.c
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+@@ -269,8 +269,7 @@ static inline void *get_freepointer(stru
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+
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+ static void prefetch_freepointer(const struct kmem_cache *s, void *object)
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+ {
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+- if (object)
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+- prefetch(freelist_dereference(s, object + s->offset));
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++ prefetch(object + s->offset);
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+ }
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+
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+ static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
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