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authorQian Cai <cai@lca.pw>2020-04-06 20:10:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-07 10:43:43 -0700
commit7e2345200262e4a6056580f0231cccdaffc825f3 (patch)
treee980a0ed03da8a98391c572545d96010d6730c0a
parent505a0ef15f96c6c43ec719c9fc1833d98957bb39 (diff)
percpu_counter: fix a data race at vm_committed_as
"vm_committed_as.count" could be accessed concurrently as reported by KCSAN, BUG: KCSAN: data-race in __vm_enough_memory / percpu_counter_add_batch write to 0xffffffff9451c538 of 8 bytes by task 65879 on cpu 35: percpu_counter_add_batch+0x83/0xd0 percpu_counter_add_batch at lib/percpu_counter.c:91 __vm_enough_memory+0xb9/0x260 dup_mm+0x3a4/0x8f0 copy_process+0x2458/0x3240 _do_fork+0xaa/0x9f0 __do_sys_clone+0x125/0x160 __x64_sys_clone+0x70/0x90 do_syscall_64+0x91/0xb05 entry_SYSCALL_64_after_hwframe+0x49/0xbe read to 0xffffffff9451c538 of 8 bytes by task 66773 on cpu 19: __vm_enough_memory+0x199/0x260 percpu_counter_read_positive at include/linux/percpu_counter.h:81 (inlined by) __vm_enough_memory at mm/util.c:839 mmap_region+0x1b2/0xa10 do_mmap+0x45c/0x700 vm_mmap_pgoff+0xc0/0x130 ksys_mmap_pgoff+0x6e/0x300 __x64_sys_mmap+0x33/0x40 do_syscall_64+0x91/0xb05 entry_SYSCALL_64_after_hwframe+0x49/0xbe The read is outside percpu_counter::lock critical section which results in a data race. Fix it by adding a READ_ONCE() in percpu_counter_read_positive() which could also service as the existing compiler memory barrier. Signed-off-by: Qian Cai <cai@lca.pw> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Marco Elver <elver@google.com> Link: http://lkml.kernel.org/r/1582302724-2804-1-git-send-email-cai@lca.pw Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/percpu_counter.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 4f052496cdfd..0a4f54dd4737 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -78,9 +78,9 @@ static inline s64 percpu_counter_read(struct percpu_counter *fbc)
*/
static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
{
- s64 ret = fbc->count;
+ /* Prevent reloads of fbc->count */
+ s64 ret = READ_ONCE(fbc->count);
- barrier(); /* Prevent reloads of fbc->count */
if (ret >= 0)
return ret;
return 0;