linux-kernel - [PATCH] sbitmap: Protect swap

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Date:   Mon, 14 Jan 2019 12:25:40 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Clark Williams <williams@...hat.com>,
        Bart Van Assche <bvanassche@....org>,
        Ming Lei <ming.lei@...hat.com>
Subject: [PATCH] sbitmap: Protect swap_lock from softirqs

From: Steven Rostedt (VMware) <rostedt@...dmis.org>

The swap_lock used by sbitmap has a chain with locks taken from
softirq, but the swap_lock is not protected from being preempted by
softirqs.

A chain exists of:

 sbq->ws[i].wait -> dispatch_wait_lock -> swap_lock

Where the sbq->ws[i].wait lock can be taken from softirq context, which
means all locks below it in the chain must also be protected from
softirqs.

Cc: stable@...r.kernel.org
Reported-by: Clark Williams <williams@...hat.com>
Fixes: 58ab5e32e6fd ("sbitmap: silence bogus lockdep IRQ warning")
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 65c2d06250a6..864354000e04 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -26,14 +26,9 @@
 static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
 {
 	unsigned long mask, val;
-	unsigned long __maybe_unused flags;
 	bool ret = false;
 
-	/* Silence bogus lockdep warning */
-#if defined(CONFIG_LOCKDEP)
-	local_irq_save(flags);
-#endif
-	spin_lock(&sb->map[index].swap_lock);
+	spin_lock_bh(&sb->map[index].swap_lock);
 
 	if (!sb->map[index].cleared)
 		goto out_unlock;
@@ -54,10 +49,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
 
 	ret = true;
 out_unlock:
-	spin_unlock(&sb->map[index].swap_lock);
-#if defined(CONFIG_LOCKDEP)
-	local_irq_restore(flags);
-#endif
+	spin_unlock_bh(&sb->map[index].swap_lock);
 	return ret;
 }