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authorDmitry Vyukov <dvyukov@google.com>2015-09-17 17:17:10 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-10-04 19:03:40 +0100
commitfacd885c75067c2a88b72622dfb0fa4b9510da5e (patch)
tree836619d525c9ef7ee3827d6387b7b05ec2389e0d
parent9e6b7cd7e77d4ca43b57c726d9bfa86d06e0567f (diff)
downloadlinux-facd885c75067c2a88b72622dfb0fa4b9510da5e.tar.bz2
tty: fix data race on tty_buffer.commit
Race on buffer data happens when newly committed data is picked up by an old flush work in the following scenario: __tty_buffer_request_room does a plain write of tail->commit, no barriers were executed before that. At this point flush_to_ldisc reads this new value of commit, and reads buffer data, no barriers in between. The committed buffer data is not necessary visible to flush_to_ldisc. Similar bug happens when tty_schedule_flip commits data. Update commit with smp_store_release and read commit with smp_load_acquire, as it is commit that signals data readiness. This is orthogonal to the existing synchronization on tty_buffer.next, which is required to not dismiss a buffer with unconsumed data. The data race was found with KernelThreadSanitizer (KTSAN). Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/tty_buffer.c15
1 files changed, 12 insertions, 3 deletions
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index b3a5e33948c1..a660ab181cca 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -293,7 +293,10 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size,
if (n != NULL) {
n->flags = flags;
buf->tail = n;
- b->commit = b->used;
+ /* paired w/ acquire in flush_to_ldisc(); ensures
+ * flush_to_ldisc() sees buffer data.
+ */
+ smp_store_release(&b->commit, b->used);
/* paired w/ acquire in flush_to_ldisc(); ensures the
* latest commit value can be read before the head is
* advanced to the next buffer
@@ -396,7 +399,10 @@ void tty_schedule_flip(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
- buf->tail->commit = buf->tail->used;
+ /* paired w/ acquire in flush_to_ldisc(); ensures
+ * flush_to_ldisc() sees buffer data.
+ */
+ smp_store_release(&buf->tail->commit, buf->tail->used);
schedule_work(&buf->work);
}
EXPORT_SYMBOL(tty_schedule_flip);
@@ -494,7 +500,10 @@ static void flush_to_ldisc(struct work_struct *work)
* is advancing to the next buffer
*/
next = smp_load_acquire(&head->next);
- count = head->commit - head->read;
+ /* paired w/ release in __tty_buffer_request_room() or in
+ * tty_buffer_flush(); ensures we see the committed buffer data
+ */
+ count = smp_load_acquire(&head->commit) - head->read;
if (!count) {
if (next == NULL) {
check_other_closed(tty);