Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934370Ab0HDVPM (ORCPT ); Wed, 4 Aug 2010 17:15:12 -0400 Received: from gate.lvk.cs.msu.su ([158.250.17.1]:54004 "EHLO mail.lvk.cs.msu.su" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759069Ab0HDVN6 (ORCPT ); Wed, 4 Aug 2010 17:13:58 -0400 X-Spam-ASN: From: Alexander Gordeev To: linux-kernel@vger.kernel.org Cc: "Nikita V\. Youshchenko" , linuxpps@ml.enneenne.com, Rodolfo Giometti , john stultz , Alexander Gordeev , Andrew Morton , Tejun Heo , Joonwoo Park Subject: [PATCHv3 03/16] pps: fix race in PPS_FETCH handler Date: Thu, 5 Aug 2010 01:06:40 +0400 Message-Id: <033148d225d9e4929fcc02ed8de0fcfa3637cffe.1280952801.git.lasaine@lvk.cs.msu.su> X-Mailer: git-send-email 1.7.1 In-Reply-To: References: X-AV-Checked: ClamAV using ClamSMTP Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3091 Lines: 93 There was a race in PPS_FETCH ioctl handler when several processes want to obtain PPS data simultaneously using sleeping PPS_FETCH. They all sleep most of the time in the system call. With the old approach when the first process waiting on the pps queue is waken up it makes new system call right away and zeroes pps->go. So other processes continue to sleep. This is a clear race condition because of the global 'go' variable. With the new approach pps->last_ev holds some value increasing at each PPS event. PPS_FETCH ioctl handler saves current value to the local variable at the very beginning so it can safely check that there is a new event by just comparing both variables. Signed-off-by: Alexander Gordeev --- drivers/pps/kapi.c | 4 ++-- drivers/pps/pps.c | 10 +++++++--- include/linux/pps_kernel.h | 2 +- 3 files changed, 10 insertions(+), 6 deletions(-) diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c index 55f3961..3f89f5e 100644 --- a/drivers/pps/kapi.c +++ b/drivers/pps/kapi.c @@ -326,8 +326,8 @@ void pps_event(int source, struct pps_ktime *ts, int event, void *data) /* Wake up if captured something */ if (captured) { - pps->go = ~0; - wake_up_interruptible(&pps->queue); + pps->last_ev++; + wake_up_interruptible_all(&pps->queue); kill_fasync(&pps->async_queue, SIGIO, POLL_IN); } diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c index c76afb9..cb24147 100644 --- a/drivers/pps/pps.c +++ b/drivers/pps/pps.c @@ -136,6 +136,7 @@ static long pps_cdev_ioctl(struct file *file, case PPS_FETCH: { struct pps_fdata fdata; + unsigned int ev; pr_debug("PPS_FETCH: source %d\n", pps->id); @@ -143,11 +144,12 @@ static long pps_cdev_ioctl(struct file *file, if (err) return -EFAULT; - pps->go = 0; + ev = pps->last_ev; /* Manage the timeout */ if (fdata.timeout.flags & PPS_TIME_INVALID) - err = wait_event_interruptible(pps->queue, pps->go); + err = wait_event_interruptible(pps->queue, + ev < pps->last_ev); else { unsigned long ticks; @@ -159,7 +161,9 @@ static long pps_cdev_ioctl(struct file *file, if (ticks != 0) { err = wait_event_interruptible_timeout( - pps->queue, pps->go, ticks); + pps->queue, + ev < pps->last_ev, + ticks); if (err == 0) return -ETIMEDOUT; } diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h index c930d11..c3aed4b 100644 --- a/include/linux/pps_kernel.h +++ b/include/linux/pps_kernel.h @@ -55,7 +55,7 @@ struct pps_device { struct pps_ktime clear_tu; int current_mode; /* PPS mode at event time */ - int go; /* PPS event is arrived? */ + unsigned int last_ev; /* last PPS event id */ wait_queue_head_t queue; /* PPS event queue */ unsigned int id; /* PPS source unique ID */ -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/