From: Roland McGrath Date: Thu, 20 Oct 2005 05:21:23 +0000 (-0700) Subject: [PATCH] Fix cpu timers exit deadlock and races X-Git-Tag: v2.6.14-rc5~15 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e03d13e985d48ac4885382c9e3b1510c78bd047f;p=pandora-kernel.git [PATCH] Fix cpu timers exit deadlock and races Oleg Nesterov reported an SMP deadlock. If there is a running timer tracking a different process's CPU time clock when the process owning the timer exits, we deadlock on tasklist_lock in posix_cpu_timer_del via exit_itimers. That code was using tasklist_lock to check for a race with __exit_signal being called on the timer-target task and clearing its ->signal. However, there is actually no such race. __exit_signal will have called posix_cpu_timers_exit and posix_cpu_timers_exit_group before it does that. Those will clear those k_itimer's association with the dying task, so posix_cpu_timer_del will return early and never reach the code in question. In addition, posix_cpu_timer_del called from exit_itimers during execve or directly from timer_delete in the process owning the timer can race with an exiting timer-target task to cause a double put on timer-target task struct. Make sure we always access cpu_timers lists with sighand lock held. Signed-off-by: Roland McGrath Signed-off-by: Chris Wright Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed