From 0462194d358c2e040282d4d1a4fd1aab84417e42 Mon Sep 17 00:00:00 2001 From: Simon Derr Date: Mon, 17 Sep 2012 15:16:28 +0200 Subject: 9P: Fix race in p9_read_work() Race scenario between p9_read_work() and p9_poll_mux() Data arrive, Rworksched is set, p9_read_work() is called. thread A thread B p9_read_work() . reads data . checks if new data ready. No. . gets preempted . More data arrive, p9_poll_mux() is called. . . . p9_poll_mux() . . if (!test_and_set_bit(Rworksched, . &m->wsched)) { . schedule_work(&m->rq); . } . . -> does not schedule work because . Rworksched is set . . clear_bit(Rworksched, &m->wsched); return; No work has been scheduled, and yet data are waiting. Currently p9_read_work() checks if there is data to read, and if not, it clears Rworksched. I think it should clear Rworksched first, and then check if there is data to read. Signed-off-by: Simon Derr Signed-off-by: Eric Van Hensbergen --- net/9p/trans_fd.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'net/9p') diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index 6449bae1570..de1bbad0c7d 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -316,8 +316,7 @@ static void p9_read_work(struct work_struct *work) m->rsize - m->rpos); p9_debug(P9_DEBUG_TRANS, "mux %p got %d bytes\n", m, err); if (err == -EAGAIN) { - clear_bit(Rworksched, &m->wsched); - return; + goto end_clear; } if (err <= 0) @@ -379,19 +378,20 @@ static void p9_read_work(struct work_struct *work) m->req = NULL; } +end_clear: + clear_bit(Rworksched, &m->wsched); + if (!list_empty(&m->req_list)) { if (test_and_clear_bit(Rpending, &m->wsched)) n = POLLIN; else n = p9_fd_poll(m->client, NULL); - if (n & POLLIN) { + if ((n & POLLIN) && !test_and_set_bit(Rworksched, &m->wsched)) { p9_debug(P9_DEBUG_TRANS, "sched read work %p\n", m); schedule_work(&m->rq); - } else - clear_bit(Rworksched, &m->wsched); - } else - clear_bit(Rworksched, &m->wsched); + } + } return; error: -- cgit v1.2.3-70-g09d2