Commit 74e72f89 authored Jan 14, 2014 by Ming Lei Committed by Linus Torvalds Jan 15, 2014

lib/percpu_counter.c: fix __percpu_counter_add()



__percpu_counter_add() may be called in softirq/hardirq handler (such
as, blk_mq_queue_exit() is typically called in hardirq/softirq handler),
so we need to call this_cpu_add()(irq safe helper) to update percpu
counter, otherwise counts may be lost.

This fixes the problem that 'rmmod null_blk' hangs in blk_cleanup_queue()
because of miscounting of request_queue->mq_usage_counter.

This patch is the v1 of previous one of "lib/percpu_counter.c:
disable local irq when updating percpu couter", and takes Andrew's
approach which may be more efficient for ARCHs(x86, s390) that
have optimized this_cpu_add().

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Shaohua Li <shli@fusionio.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Fan Du <fan.du@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5a610fcc

lib/percpu_counter.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -82,10 +82,10 @@ void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
		unsigned long flags;
		raw_spin_lock_irqsave(&fbc->lock, flags);
		fbc->count += count;
		__this_cpu_sub(*fbc->counters, count);
		raw_spin_unlock_irqrestore(&fbc->lock, flags);
		__this_cpu_write(*fbc->counters, 0);
		} else {
		__this_cpu_write(*fbc->counters, count);
		this_cpu_add(*fbc->counters, amount);
		}
		preempt_enable();
		}

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