[PATCH v5] mm,hwpoison: send SIGBUS to PF_MCE_EARLY processes on action required events

* [PATCH v5] mm,hwpoison: send SIGBUS to PF_MCE_EARLY processes on action required events
@ 2021-01-20  8:24 Aili Yao
  2021-01-21 10:03 ` Oscar Salvador
  0 siblings, 1 reply; 3+ messages in thread
From: Aili Yao @ 2021-01-20  8:24 UTC (permalink / raw)
  To: naoya.horiguchi, linux-mm, osalvador, YANGFENG1

When a memory uncorrected error is triggered by process who accessed
the address with error, It's Action Required Case for only current
process which triggered this; This Action Required case means Action
optional to other process who share the same page. Usually killing
current process will be sufficient, other processes sharing the same
page will get be signaled when they really touch the poisoned page.

But there is another scenario that other processes
sharing the same page want to be signaled early with PF_MCE_EARLY set,
In this case, we should get them into kill list and signal
BUS_MCEERR_AO to them.

So in this patch, task_early_kill will check current process if
force_early is set, and if not current,the code will fallback to
find_early_kill_thread() to check if there is PF_MCE_EARLY process
who cares the error.

In kill_proc(), BUS_MCEERR_AR is only send to current, other processes in
kill list will be signaled with BUS_MCEERR_AO.

Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
---
 mm/memory-failure.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 5a38e9eade94..441fe2787cd4 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -243,9 +243,12 @@ static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
 			pfn, t->comm, t->pid);
 
 	if (flags & MF_ACTION_REQUIRED) {
-		WARN_ON_ONCE(t != current);
-		ret = force_sig_mceerr(BUS_MCEERR_AR,
+		if (tk->tsk == current)
+			ret = force_sig_mceerr(BUS_MCEERR_AR,
 					 (void __user *)tk->addr, addr_lsb);
+		else
+			ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
+				addr_lsb, t);
 	} else {
 		/*
 		 * Don't use force here, it's convenient if the signal
@@ -440,10 +443,13 @@ static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
  * Determine whether a given process is "early kill" process which expects
  * to be signaled when some page under the process is hwpoisoned.
  * Return task_struct of the dedicated thread (main thread unless explicitly
- * specified) if the process is "early kill," and otherwise returns NULL.
+ * specified) if the process is "early kill" and otherwise returns NULL.
  *
- * Note that the above is true for Action Optional case, but not for Action
- * Required case where SIGBUS should sent only to the current thread.
+ * Note that the above is true for Action Optional case. For Action Required
+ * case, it's only meaningful to the current thread which need to be signaled
+ * with SIGBUS, this error is Action Optional for other non current
+ * processes sharing the same error page,if the process is "early kill", the
+ * task_struct of the dedicated thread will also be returned.
  */
 static struct task_struct *task_early_kill(struct task_struct *tsk,
 					   int force_early)
@@ -457,8 +463,6 @@ static struct task_struct *task_early_kill(struct task_struct *tsk,
 		 */
 		if (tsk->mm == current->mm)
 			return current;
-		else
-			return NULL;
 	}
 	return find_early_kill_thread(tsk);
 }
-- 
2.25.1



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