blob: bd68ff2edeb4667297ebe16f1c991db2edfa8e80 [file] [log] [blame]
From c3e917377562343369ac0d5db184a23b3797f8e7 Mon Sep 17 00:00:00 2001
From: Barret Rhoden <brho@google.com>
Date: Tue, 14 Apr 2020 18:29:20 -0400
Subject: [PATCH] perf: Add cond_resched() to task_function_call()
commit 2ed6edd33a214bca02bd2b45e3fc3038a059436b upstream.
Under rare circumstances, task_function_call() can repeatedly fail and
cause a soft lockup.
There is a slight race where the process is no longer running on the cpu
we targeted by the time remote_function() runs. The code will simply
try again. If we are very unlucky, this will continue to fail, until a
watchdog fires. This can happen in a heavily loaded, multi-core virtual
machine.
Reported-by: syzbot+bb4935a5c09b5ff79940@syzkaller.appspotmail.com
Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200414222920.121401-1-brho@google.com
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ab650d239094..0e6168c4cb7a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -93,11 +93,11 @@ static void remote_function(void *data)
* @info: the function call argument
*
* Calls the function @func when the task is currently running. This might
- * be on the current CPU, which just calls the function directly
+ * be on the current CPU, which just calls the function directly. This will
+ * retry due to any failures in smp_call_function_single(), such as if the
+ * task_cpu() goes offline concurrently.
*
- * returns: @func return value, or
- * -ESRCH - when the process isn't running
- * -EAGAIN - when the process moved away
+ * returns @func return value or -ESRCH when the process isn't running
*/
static int
task_function_call(struct task_struct *p, remote_function_f func, void *info)
@@ -110,11 +110,16 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info)
};
int ret;
- do {
- ret = smp_call_function_single(task_cpu(p), remote_function, &data, 1);
- if (!ret)
- ret = data.ret;
- } while (ret == -EAGAIN);
+ for (;;) {
+ ret = smp_call_function_single(task_cpu(p), remote_function,
+ &data, 1);
+ ret = !ret ? data.ret : -EAGAIN;
+
+ if (ret != -EAGAIN)
+ break;
+
+ cond_resched();
+ }
return ret;
}
--
2.27.0