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由 Sergey Senozhatsky 提交于
Commit 4221a991 "Add RCU check for find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns. Add rcu_read_lock/rcu_read_unlock to call find_task_by_vpid. Tetsuo Handa wrote: | Quoting from one of posts in that thead | http://kerneltrap.org/mailarchive/linux-kernel/2010/2/8/4536388 | || Usually tasklist gives enough protection, but if copy_process() fails || it calls free_pid() lockless and does call_rcu(delayed_put_pid(). || This means, without rcu lock find_pid_ns() can't scan the hash table || safely. Thomas Gleixner wrote: | We can remove the tasklist_lock while at it. rcu_read_lock is enough. Patch also replaces thread_group_leader with has_group_leader_pid in accordance to comment by Oleg Nesterov: | ... thread_group_leader() check is not relaible without | tasklist. If we race with de_thread() find_task_by_vpid() can find | the new leader before it updates its ->group_leader. | | perhaps it makes sense to change posix_cpu_timer_create() to use | has_group_leader_pid() instead, just to make this code not look racy | and avoid adding new problems. Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Stanislaw Gruszka <sgruszka@redhat.com> Reviewed-by: NOleg Nesterov <oleg@redhat.com> LKML-Reference: <20101103165256.GD30053@swordfish.minsk.epam.com> Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
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