Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 16/19] mm: prevent mmap_cache race in find_vma() | Date | Wed, 10 Apr 2013 15:50:39 -0700 |
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3.0-stable review patch. If anyone has any objections, please let me know.
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From: Jan Stancek <jstancek@redhat.com>
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/mmap.c | 2 +- mm/nommu.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
--- a/mm/mmap.c +++ b/mm/mmap.c @@ -1581,7 +1581,7 @@ struct vm_area_struct *find_vma(struct m 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; --- a/mm/nommu.c +++ b/mm/nommu.c @@ -808,7 +808,7 @@ struct vm_area_struct *find_vma(struct m struct vm_area_struct *vma; /* check the cache first */ - vma = mm->mmap_cache; + vma = ACCESS_ONCE(mm->mmap_cache); if (vma && vma->vm_start <= addr && vma->vm_end > addr) return vma;
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