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authorQian Cai <cai@lca.pw>2020-02-11 14:54:15 +0100
committerPaul E. McKenney <paulmck@kernel.org>2020-06-29 21:04:48 +0200
commit33190b675ce2eacbeb4e75168c05b41110b506ec (patch)
treec1290359ba769363b2d0bdbaebd169b86d716b85 /kernel/locking
parentkcsan: Add test suite (diff)
downloadlinux-33190b675ce2eacbeb4e75168c05b41110b506ec.tar.xz
linux-33190b675ce2eacbeb4e75168c05b41110b506ec.zip
locking/osq_lock: Annotate a data race in osq_lock
The prev->next pointer can be accessed concurrently as noticed by KCSAN: write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107: osq_lock+0x25f/0x350 osq_wait_next at kernel/locking/osq_lock.c:79 (inlined by) osq_lock at kernel/locking/osq_lock.c:185 rwsem_optimistic_spin <snip> read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100: osq_lock+0x196/0x350 osq_lock at kernel/locking/osq_lock.c:157 rwsem_optimistic_spin <snip> Since the write only stores NULL to prev->next and the read tests if prev->next equals to this_cpu_ptr(&osq_node). Even if the value is shattered, the code is still working correctly. Thus, mark it as an intentional data race using the data_race() macro. Signed-off-by: Qian Cai <cai@lca.pw> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/osq_lock.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 1f7734949ac8..1de006ed3aa8 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -154,7 +154,11 @@ bool osq_lock(struct optimistic_spin_queue *lock)
*/
for (;;) {
- if (prev->next == node &&
+ /*
+ * cpu_relax() below implies a compiler barrier which would
+ * prevent this comparison being optimized away.
+ */
+ if (data_race(prev->next) == node &&
cmpxchg(&prev->next, node, NULL) == node)
break;