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authorDave Hansen <dave.hansen@linux.intel.com>2014-01-30 15:46:09 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-30 16:56:56 -0800
commita03208652dad18232e9ec3432df69f9c19c856ec (patch)
treee11b60229136b2a62dc0683e3a684d105cd6defc /mm
parent8790c71a18e5d2d93532ae250bcf5eddbba729cd (diff)
downloadlinux-a03208652dad18232e9ec3432df69f9c19c856ec.tar.gz
mm/slub.c: fix page->_count corruption (again)
Commit abca7c496584 ("mm: fix slab->page _count corruption when using slub") notes that we can not _set_ a page->counters directly, except when using a real double-cmpxchg. Doing so can lose updates to ->_count. That is an absolute rule: You may not *set* page->counters except via a cmpxchg. Commit abca7c496584 fixed this for the folks who have the slub cmpxchg_double code turned off at compile time, but it left the bad case alone. It can still be reached, and the same bug triggered in two cases: 1. Turning on slub debugging at runtime, which is available on the distro kernels that I looked at. 2. On 64-bit CPUs with no CMPXCHG16B (some early AMD x86-64 cpus, evidently) There are at least 3 ways we could fix this: 1. Take all of the exising calls to cmpxchg_double_slab() and __cmpxchg_double_slab() and convert them to take an old, new and target 'struct page'. 2. Do (1), but with the newly-introduced 'slub_data'. 3. Do some magic inside the two cmpxchg...slab() functions to pull the counters out of new_counters and only set those fields in page->{inuse,frozen,objects}. I've done (2) as well, but it's a bunch more code. This patch is an attempt at (3). This was the most straightforward and foolproof way that I could think to do this. This would also technically allow us to get rid of the ugly #if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \ defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE) in 'struct page', but leaving it alone has the added benefit that 'counters' stays 'unsigned' instead of 'unsigned long', so all the copies that the slub code does stay a bit smaller. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: Pekka Enberg <penberg@kernel.org> Cc: Matt Mackall <mpm@selenic.com> Cc: Pravin B Shelar <pshelar@nicira.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/slub.c19
1 files changed, 17 insertions, 2 deletions
diff --git a/mm/slub.c b/mm/slub.c
index 545a170ebf9..2b1a6970e46 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -355,6 +355,21 @@ static __always_inline void slab_unlock(struct page *page)
__bit_spin_unlock(PG_locked, &page->flags);
}
+static inline void set_page_slub_counters(struct page *page, unsigned long counters_new)
+{
+ struct page tmp;
+ tmp.counters = counters_new;
+ /*
+ * page->counters can cover frozen/inuse/objects as well
+ * as page->_count. If we assign to ->counters directly
+ * we run the risk of losing updates to page->_count, so
+ * be careful and only assign to the fields we need.
+ */
+ page->frozen = tmp.frozen;
+ page->inuse = tmp.inuse;
+ page->objects = tmp.objects;
+}
+
/* Interrupts must be disabled (for the fallback code to work right) */
static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
void *freelist_old, unsigned long counters_old,
@@ -376,7 +391,7 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page
if (page->freelist == freelist_old &&
page->counters == counters_old) {
page->freelist = freelist_new;
- page->counters = counters_new;
+ set_page_slub_counters(page, counters_new);
slab_unlock(page);
return 1;
}
@@ -415,7 +430,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
if (page->freelist == freelist_old &&
page->counters == counters_old) {
page->freelist = freelist_new;
- page->counters = counters_new;
+ set_page_slub_counters(page, counters_new);
slab_unlock(page);
local_irq_restore(flags);
return 1;