Commit 37198768 authored Jan 14, 2019 by Steven Rostedt (VMware) Committed by Linus Torvalds Jan 15, 2019

sbitmap: Protect swap_lock from softirqs



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.

Reported-by: Clark Williams <williams@redhat.com>
Fixes: 58ab5e32 ("sbitmap: silence bogus lockdep IRQ warning")
Fixes: ea86ea2c ("sbitmap: amortize cost of clearing bits")
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c962cb32

lib/sbitmap.c

+2 −10

Original line number	Diff line number	Diff line
		@@ -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;
		}

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