3.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jan Stancek <jstancek@xxxxxxxxxx>
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@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 2 +-
mm/nommu.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1922,7 +1922,7 @@ struct vm_area_struct *find_vma(struct m
/* 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
@@ -819,7 +819,7 @@ 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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