Alexander Gordeev 3003d55b59 pps: fix race in PPS_FETCH handler ... 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>		2011-01-13 08:03:19 -08:00
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clients	pps: serial clients support	2010-03-12 15:52:43 -08:00
kapi.c	pps: fix race in PPS_FETCH handler	2011-01-13 08:03:19 -08:00
Kconfig	pps: LinuxPPS clients support	2010-03-12 15:52:43 -08:00
Makefile	pps: LinuxPPS clients support	2010-03-12 15:52:43 -08:00
pps.c	pps: fix race in PPS_FETCH handler	2011-01-13 08:03:19 -08:00
sysfs.c	LinuxPPS: core support	2009-06-18 13:04:04 -07:00