Commit 1c089129 authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Greg Kroah-Hartman
Browse files

lib/ratelimit.c: use deferred printk() version

commit 656d61ce upstream.

printk_ratelimit() invokes ___ratelimit() which may invoke a normal
printk() (pr_warn() in this particular case) to warn about suppressed
output.  Given that printk_ratelimit() may be called from anywhere, that
pr_warn() is dangerous - it may end up deadlocking the system.  Fix
___ratelimit() by using deferred printk().

Sasha reported the following lockdep error:

 : Unregister pv shared memory for cpu 8
 : select_fallback_rq: 3 callbacks suppressed
 : process 8583 (trinity-c78) no longer affine to cpu8
 :
 : ======================================================
 : WARNING: possible circular locking dependency detected
 : 4.14.0-rc2-next-20170927+ #252 Not tainted
 : ------------------------------------------------------
 : migration/8/62 is trying to acquire lock:
 : (&port_lock_key){-.-.}, at: serial8250_console_write()
 :
 : but task is already holding lock:
 : (&rq->lock){-.-.}, at: sched_cpu_dy...
parent 2b819707
......@@ -48,7 +48,9 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
if (time_is_before_jiffies(rs->begin + rs->interval)) {
if (rs->missed) {
if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) {
pr_warn("%s: %d callbacks suppressed\n", func, rs->missed);
printk_deferred(KERN_WARNING
"%s: %d callbacks suppressed\n",
func, rs->missed);
rs->missed = 0;
}
}
......
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