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 <lasaine@lvk.cs.msu.su> Acked-by: Rodolfo Giometti <giometti@linux.it> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
324 lines
7.1 KiB
C
324 lines
7.1 KiB
C
/*
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* PPS core file
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*
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*
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* Copyright (C) 2005-2009 Rodolfo Giometti <giometti@linux.it>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/sched.h>
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#include <linux/uaccess.h>
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#include <linux/idr.h>
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#include <linux/cdev.h>
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#include <linux/poll.h>
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#include <linux/pps_kernel.h>
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/*
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* Local variables
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*/
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static dev_t pps_devt;
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static struct class *pps_class;
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/*
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* Char device methods
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*/
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static unsigned int pps_cdev_poll(struct file *file, poll_table *wait)
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{
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struct pps_device *pps = file->private_data;
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poll_wait(file, &pps->queue, wait);
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return POLLIN | POLLRDNORM;
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}
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static int pps_cdev_fasync(int fd, struct file *file, int on)
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{
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struct pps_device *pps = file->private_data;
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return fasync_helper(fd, file, on, &pps->async_queue);
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}
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static long pps_cdev_ioctl(struct file *file,
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unsigned int cmd, unsigned long arg)
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{
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struct pps_device *pps = file->private_data;
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struct pps_kparams params;
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void __user *uarg = (void __user *) arg;
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int __user *iuarg = (int __user *) arg;
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int err;
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switch (cmd) {
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case PPS_GETPARAMS:
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pr_debug("PPS_GETPARAMS: source %d\n", pps->id);
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spin_lock_irq(&pps->lock);
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/* Get the current parameters */
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params = pps->params;
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spin_unlock_irq(&pps->lock);
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err = copy_to_user(uarg, ¶ms, sizeof(struct pps_kparams));
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if (err)
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return -EFAULT;
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break;
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case PPS_SETPARAMS:
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pr_debug("PPS_SETPARAMS: source %d\n", pps->id);
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/* Check the capabilities */
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if (!capable(CAP_SYS_TIME))
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return -EPERM;
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err = copy_from_user(¶ms, uarg, sizeof(struct pps_kparams));
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if (err)
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return -EFAULT;
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if (!(params.mode & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR))) {
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pr_debug("capture mode unspecified (%x)\n",
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params.mode);
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return -EINVAL;
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}
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/* Check for supported capabilities */
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if ((params.mode & ~pps->info.mode) != 0) {
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pr_debug("unsupported capabilities (%x)\n",
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params.mode);
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return -EINVAL;
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}
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spin_lock_irq(&pps->lock);
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/* Save the new parameters */
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pps->params = params;
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/* Restore the read only parameters */
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if ((params.mode & (PPS_TSFMT_TSPEC | PPS_TSFMT_NTPFP)) == 0) {
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/* section 3.3 of RFC 2783 interpreted */
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pr_debug("time format unspecified (%x)\n",
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params.mode);
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pps->params.mode |= PPS_TSFMT_TSPEC;
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}
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if (pps->info.mode & PPS_CANWAIT)
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pps->params.mode |= PPS_CANWAIT;
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pps->params.api_version = PPS_API_VERS;
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spin_unlock_irq(&pps->lock);
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break;
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case PPS_GETCAP:
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pr_debug("PPS_GETCAP: source %d\n", pps->id);
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err = put_user(pps->info.mode, iuarg);
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if (err)
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return -EFAULT;
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break;
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case PPS_FETCH: {
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struct pps_fdata fdata;
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unsigned int ev;
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pr_debug("PPS_FETCH: source %d\n", pps->id);
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err = copy_from_user(&fdata, uarg, sizeof(struct pps_fdata));
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if (err)
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return -EFAULT;
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ev = pps->last_ev;
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/* Manage the timeout */
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if (fdata.timeout.flags & PPS_TIME_INVALID)
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err = wait_event_interruptible(pps->queue,
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ev != pps->last_ev);
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else {
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unsigned long ticks;
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pr_debug("timeout %lld.%09d\n",
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(long long) fdata.timeout.sec,
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fdata.timeout.nsec);
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ticks = fdata.timeout.sec * HZ;
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ticks += fdata.timeout.nsec / (NSEC_PER_SEC / HZ);
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if (ticks != 0) {
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err = wait_event_interruptible_timeout(
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pps->queue,
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ev != pps->last_ev,
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ticks);
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if (err == 0)
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return -ETIMEDOUT;
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}
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}
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/* Check for pending signals */
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if (err == -ERESTARTSYS) {
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pr_debug("pending signal caught\n");
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return -EINTR;
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}
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/* Return the fetched timestamp */
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spin_lock_irq(&pps->lock);
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fdata.info.assert_sequence = pps->assert_sequence;
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fdata.info.clear_sequence = pps->clear_sequence;
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fdata.info.assert_tu = pps->assert_tu;
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fdata.info.clear_tu = pps->clear_tu;
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fdata.info.current_mode = pps->current_mode;
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spin_unlock_irq(&pps->lock);
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err = copy_to_user(uarg, &fdata, sizeof(struct pps_fdata));
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if (err)
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return -EFAULT;
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break;
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}
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default:
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return -ENOTTY;
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break;
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}
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return 0;
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}
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static int pps_cdev_open(struct inode *inode, struct file *file)
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{
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struct pps_device *pps = container_of(inode->i_cdev,
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struct pps_device, cdev);
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int found;
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found = pps_get_source(pps->id) != 0;
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if (!found)
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return -ENODEV;
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file->private_data = pps;
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return 0;
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}
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static int pps_cdev_release(struct inode *inode, struct file *file)
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{
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struct pps_device *pps = file->private_data;
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/* Free the PPS source and wake up (possible) deregistration */
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pps_put_source(pps);
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return 0;
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}
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/*
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* Char device stuff
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*/
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static const struct file_operations pps_cdev_fops = {
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.owner = THIS_MODULE,
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.llseek = no_llseek,
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.poll = pps_cdev_poll,
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.fasync = pps_cdev_fasync,
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.unlocked_ioctl = pps_cdev_ioctl,
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.open = pps_cdev_open,
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.release = pps_cdev_release,
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};
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int pps_register_cdev(struct pps_device *pps)
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{
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int err;
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pps->devno = MKDEV(MAJOR(pps_devt), pps->id);
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cdev_init(&pps->cdev, &pps_cdev_fops);
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pps->cdev.owner = pps->info.owner;
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err = cdev_add(&pps->cdev, pps->devno, 1);
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if (err) {
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printk(KERN_ERR "pps: %s: failed to add char device %d:%d\n",
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pps->info.name, MAJOR(pps_devt), pps->id);
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return err;
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}
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pps->dev = device_create(pps_class, pps->info.dev, pps->devno, NULL,
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"pps%d", pps->id);
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if (IS_ERR(pps->dev))
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goto del_cdev;
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dev_set_drvdata(pps->dev, pps);
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pr_debug("source %s got cdev (%d:%d)\n", pps->info.name,
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MAJOR(pps_devt), pps->id);
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return 0;
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del_cdev:
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cdev_del(&pps->cdev);
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return err;
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}
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void pps_unregister_cdev(struct pps_device *pps)
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{
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device_destroy(pps_class, pps->devno);
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cdev_del(&pps->cdev);
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}
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/*
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* Module stuff
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*/
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static void __exit pps_exit(void)
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{
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class_destroy(pps_class);
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unregister_chrdev_region(pps_devt, PPS_MAX_SOURCES);
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}
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static int __init pps_init(void)
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{
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int err;
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pps_class = class_create(THIS_MODULE, "pps");
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if (!pps_class) {
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printk(KERN_ERR "pps: failed to allocate class\n");
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return -ENOMEM;
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}
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pps_class->dev_attrs = pps_attrs;
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err = alloc_chrdev_region(&pps_devt, 0, PPS_MAX_SOURCES, "pps");
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if (err < 0) {
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printk(KERN_ERR "pps: failed to allocate char device region\n");
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goto remove_class;
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}
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pr_info("LinuxPPS API ver. %d registered\n", PPS_API_VERS);
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pr_info("Software ver. %s - Copyright 2005-2007 Rodolfo Giometti "
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"<giometti@linux.it>\n", PPS_VERSION);
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return 0;
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remove_class:
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class_destroy(pps_class);
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return err;
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}
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subsys_initcall(pps_init);
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module_exit(pps_exit);
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MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
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MODULE_DESCRIPTION("LinuxPPS support (RFC 2783) - ver. " PPS_VERSION);
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MODULE_LICENSE("GPL");
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