[ Upstream commit 355f074609dbf3042900ea9d30fcd2b0c323a365 ]
syzbot reported:
| BUG: KCSAN: data-race in p9_fd_create / p9_fd_create
|
| read-write to 0xffff888130fb3d48 of 4 bytes by task 15599 on cpu 0:
| p9_fd_open net/9p/trans_fd.c:842 [inline]
| p9_fd_create+0x210/0x250 net/9p/trans_fd.c:1092
| p9_client_create+0x595/0xa70 net/9p/client.c:1010
| v9fs_session_init+0xf9/0xd90 fs/9p/v9fs.c:410
| v9fs_mount+0x69/0x630 fs/9p/vfs_super.c:123
| legacy_get_tree+0x74/0xd0 fs/fs_context.c:611
| vfs_get_tree+0x51/0x190 fs/super.c:1519
| do_new_mount+0x203/0x660 fs/namespace.c:3335
| path_mount+0x496/0xb30 fs/namespace.c:3662
| do_mount fs/namespace.c:3675 [inline]
| __do_sys_mount fs/namespace.c:3884 [inline]
| [...]
|
| read-write to 0xffff888130fb3d48 of 4 bytes by task 15563 on cpu 1:
| p9_fd_open net/9p/trans_fd.c:842 [inline]
| p9_fd_create+0x210/0x250 net/9p/trans_fd.c:1092
| p9_client_create+0x595/0xa70 net/9p/client.c:1010
| v9fs_session_init+0xf9/0xd90 fs/9p/v9fs.c:410
| v9fs_mount+0x69/0x630 fs/9p/vfs_super.c:123
| legacy_get_tree+0x74/0xd0 fs/fs_context.c:611
| vfs_get_tree+0x51/0x190 fs/super.c:1519
| do_new_mount+0x203/0x660 fs/namespace.c:3335
| path_mount+0x496/0xb30 fs/namespace.c:3662
| do_mount fs/namespace.c:3675 [inline]
| __do_sys_mount fs/namespace.c:3884 [inline]
| [...]
|
| value changed: 0x00008002 -> 0x00008802
Within p9_fd_open(), O_NONBLOCK is added to f_flags of the read and
write files. This may happen concurrently if e.g. mounting process
modifies the fd in another thread.
Mark the plain read-modify-writes as intentional data-races, with the
assumption that the result of executing the accesses concurrently will
always result in the same result despite the accesses themselves not
being atomic.
Reported-by: syzbot+e441aeeb422763cc5511@syzkaller.appspotmail.com
Signed-off-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/ZO38mqkS0TYUlpFp@elver.google.com
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Message-ID: <20231025103445.1248103-1-asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
dc1f427e7d