Messages in this thread | | | Date | Fri, 20 Jan 2012 20:18:31 +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 03:15:32PM +0900, Namjae Jeon wrote: >> 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 ? > > wakeup_timer_fn() holds the wb_lock across the check for bdi->dev != > NULL and the call to trace_writeback_wake_forker_thread(), so no.
The following case is not possible with racing of __mark_inode_dirty ? -------------------------------------------------------------------------------------------------- spin_lock bdi->dev = NULL; spin_unlock spin_lock ...... ...... trace_writeback_wake_forker_thread(bdi); spin_unlock ----------------------------------------------------------------------------- -- 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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