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authorJan Stancek <jstancek@redhat.com>2013-04-04 11:35:10 -0700
committerBen Hutchings <ben@decadent.org.uk>2013-04-10 03:20:07 +0100
commitb8e35885679ef5f44dab1c100219b82eae7a1c13 (patch)
tree364a6fe85808c9cb0581d256d3715d5ff2065dfd /mm/mmap.c
parent7f23d37a2aacb81f067053955896b97cadb5a256 (diff)
mm: prevent mmap_cache race in find_vma()
commit b6a9b7f6b1f21735a7456d534dc0e68e61359d2c upstream. find_vma() can be called by multiple threads with read lock held on mm->mmap_sem and any of them can update mm->mmap_cache. Prevent compiler from re-fetching mm->mmap_cache, because other readers could update it in the meantime: thread 1 thread 2 | find_vma() | find_vma() struct vm_area_struct *vma = NULL; | vma = mm->mmap_cache; | if (!(vma && vma->vm_end > addr | && vma->vm_start <= addr)) { | | mm->mmap_cache = vma; return vma; | ^^ compiler may optimize this | local variable out and re-read | mm->mmap_cache | This issue can be reproduced with gcc-4.8.0-1 on s390x by running mallocstress testcase from LTP, which triggers: kernel BUG at mm/rmap.c:1088! Call Trace: ([<000003d100c57000>] 0x3d100c57000) [<000000000023a1c0>] do_wp_page+0x2fc/0xa88 [<000000000023baae>] handle_pte_fault+0x41a/0xac8 [<000000000023d832>] handle_mm_fault+0x17a/0x268 [<000000000060507a>] do_protection_exception+0x1e2/0x394 [<0000000000603a04>] pgm_check_handler+0x138/0x13c [<000003fffcf1f07a>] 0x3fffcf1f07a Last Breaking-Event-Address: [<000000000024755e>] page_add_new_anon_rmap+0xc2/0x168 Thanks to Jakub Jelinek for his insight on gcc and helping to track this down. Signed-off-by: Jan Stancek <jstancek@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [bwh: Backported to 3.2: adjust context, indentation] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index eae90af60ea6..dff37a686230 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1573,7 +1573,7 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
if (mm) {
/* Check the cache first. */
/* (Cache hit rate is typically around 35%.) */
- vma = mm->mmap_cache;
+ vma = ACCESS_ONCE(mm->mmap_cache);
if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
struct rb_node * rb_node;