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1effd9f193
Unlocked access to dst_rq->curr in task_numa_compare() is racy. If curr task is exiting this may be a reason of use-after-free: task_numa_compare() do_exit() ... current->flags |= PF_EXITING; ... release_task() ... ~~delayed_put_task_struct()~~ ... schedule() rcu_read_lock() ... cur = ACCESS_ONCE(dst_rq->curr) ... ... rq->curr = next; ... context_switch() ... finish_task_switch() ... put_task_struct() ... __put_task_struct() ... free_task_struct() task_numa_assign() ... get_task_struct() ... As noted by Oleg: <<The lockless get_task_struct(tsk) is only safe if tsk == current and didn't pass exit_notify(), or if this tsk was found on a rcu protected list (say, for_each_process() or find_task_by_vpid()). IOW, it is only safe if release_task() was not called before we take rcu_read_lock(), in this case we can rely on the fact that delayed_put_pid() can not drop the (potentially) last reference until rcu_read_unlock(). And as Kirill pointed out task_numa_compare()->task_numa_assign() path does get_task_struct(dst_rq->curr) and this is not safe. The task_struct itself can't go away, but rcu_read_lock() can't save us from the final put_task_struct() in finish_task_switch(); this reference goes away without rcu gp>> The patch provides simple check of PF_EXITING flag. If it's not set, this guarantees that call_rcu() of delayed_put_task_struct() callback hasn't happened yet, so we can safely do get_task_struct() in task_numa_assign(). Locked dst_rq->lock protects from concurrency with the last schedule(). Reusing or unmapping of cur's memory may happen without it. Suggested-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Kirill Tkhai <ktkhai@parallels.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1413962231.19914.130.camel@tkhai Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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.. | ||
auto_group.c | ||
auto_group.h | ||
clock.c | ||
completion.c | ||
core.c | ||
cpuacct.c | ||
cpuacct.h | ||
cpudeadline.c | ||
cpudeadline.h | ||
cpupri.c | ||
cpupri.h | ||
cputime.c | ||
deadline.c | ||
debug.c | ||
fair.c | ||
features.h | ||
idle_task.c | ||
idle.c | ||
Makefile | ||
proc.c | ||
rt.c | ||
sched.h | ||
stats.c | ||
stats.h | ||
stop_task.c | ||
wait.c |