在 2023/8/21 12:34, Matthew Wilcox 写道:
On Mon, Aug 21, 2023 at 10:25:34AM +0800, Tong Tiangen wrote:+++ b/mm/memory-failure.c @@ -546,24 +546,26 @@ static void kill_procs(struct list_head *to_kill, int forcekill, bool fail, * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO) * on behalf of the thread group. Return task_struct of the (first found) * dedicated thread if found, and return NULL otherwise. - * - * We already hold read_lock(&tasklist_lock) in the caller, so we don't - * have to call rcu_read_lock/unlock() in this function. */ static struct task_struct *find_early_kill_thread(struct task_struct *tsk) { struct task_struct *t;+ rcu_read_lock();for_each_thread(tsk, t) { if (t->flags & PF_MCE_PROCESS) { if (t->flags & PF_MCE_EARLY) - return t; + goto found; } else { if (sysctl_memory_failure_early_kill) - return t; + goto found; } } - return NULL; + + t = NULL; +found: + rcu_read_unlock(); + return t; }I don't understand why you need to modify find_early_kill_thread() at all. It's still true that the caller holds _a_ lock protecting it; the comment needs to be updated to reflect that it might be the RCU lock or the tasklist_lock (or did you change all callers?), but there's no need for this function to take the RCU lock itself, afaics? .
I've checked that all the paths that call find_early_kill_thread() already hold the rcu lock, and there's really no need to hold the rcu lock here.
In the next patch version, here only the comments are modified. Thanks, Tong.
