Messages in this thread | | | Date | Fri, 20 Jan 2012 15:15:32 +0900 | Subject | Re: [PATCHv2] backing-dev: fix wakeup timer races with bdi_unregister() | From | Namjae Jeon <> |
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2012/1/20 Rabin Vincent <rabin@rab.in>: > On Fri, Jan 20, 2012 at 05:16, Namjae Jeon <linkinjeon@gmail.com> wrote: >>> bdi_debug_unregister(bdi); >>> - device_unregister(bdi->dev); >>> + >>> + spin_lock_bh(&bdi->wb_lock); >>> bdi->dev = NULL; >>> + spin_unlock_bh(&bdi->wb_lock); >> Hi. >> Would you explain me why you add spinlock in here ? > > wakeup_timer_fn() does the following, where the > trace_writeback_wake_forker_thread() also accesses bdi->dev. > It does this under the wb_lock: > > } else if (bdi->dev) { > /* > * When bdi tasks are inactive for long time, they are killed. > * In this case we have to wake-up the forker thread which > * should create and run the bdi thread. > */ > trace_writeback_wake_forker_thread(bdi); > > If we don't have the lock above, the bdi->dev could potentially be > cleared after the check but before the tracepoint is hit, leading to a > NULL pointer dereference. Is there no possibility trace_writeback_wake_forker_thread is called after spin_unlock of bdi->de= null ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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