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https://github.com/rd-stuffs/msm-4.14.git
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3003d55b59
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>
94 lines
2.6 KiB
C
94 lines
2.6 KiB
C
/*
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* PPS API kernel header
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*
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* Copyright (C) 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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#ifndef LINUX_PPS_KERNEL_H
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#define LINUX_PPS_KERNEL_H
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#include <linux/pps.h>
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#include <linux/cdev.h>
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#include <linux/device.h>
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#include <linux/time.h>
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/*
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* Global defines
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*/
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/* The specific PPS source info */
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struct pps_source_info {
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char name[PPS_MAX_NAME_LEN]; /* simbolic name */
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char path[PPS_MAX_NAME_LEN]; /* path of connected device */
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int mode; /* PPS's allowed mode */
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void (*echo)(int source, int event, void *data); /* PPS echo function */
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struct module *owner;
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struct device *dev;
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};
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/* The main struct */
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struct pps_device {
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struct pps_source_info info; /* PSS source info */
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struct pps_kparams params; /* PPS's current params */
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__u32 assert_sequence; /* PPS' assert event seq # */
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__u32 clear_sequence; /* PPS' clear event seq # */
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struct pps_ktime assert_tu;
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struct pps_ktime clear_tu;
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int current_mode; /* PPS mode at event time */
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unsigned int last_ev; /* last PPS event id */
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wait_queue_head_t queue; /* PPS event queue */
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unsigned int id; /* PPS source unique ID */
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struct cdev cdev;
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struct device *dev;
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int devno;
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struct fasync_struct *async_queue; /* fasync method */
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spinlock_t lock;
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atomic_t usage; /* usage count */
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};
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/*
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* Global variables
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*/
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extern spinlock_t pps_idr_lock;
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extern struct idr pps_idr;
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extern struct device_attribute pps_attrs[];
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/*
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* Exported functions
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*/
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struct pps_device *pps_get_source(int source);
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extern void pps_put_source(struct pps_device *pps);
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extern int pps_register_source(struct pps_source_info *info,
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int default_params);
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extern void pps_unregister_source(int source);
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extern int pps_register_cdev(struct pps_device *pps);
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extern void pps_unregister_cdev(struct pps_device *pps);
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extern void pps_event(int source, struct pps_ktime *ts, int event, void *data);
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#endif /* LINUX_PPS_KERNEL_H */
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