On Wed, Jan 11, 2017 at 02:00:21PM +0100, iari@xxxxxx wrote: > From: Iago Abal <mail@xxxxxxxxxxx> > > The static bug finder EBA (http://www.iagoabal.eu/eba/) reported the > following double-lock bug: > > Double lock: > 1. spin_lock_irqsave(pch->lock, flags) at pl330_free_chan_resources:2236; > 2. call to function `pl330_release_channel' immediately after; > 3. call to function `dma_pl330_rqcb' in line 1753; > 4. spin_lock_irqsave(pch->lock, flags) at dma_pl330_rqcb:1505. > > I have fixed it as suggested by Marek Szyprowski. > > First, I have replaced `pch->lock' with `pl330->lock' in functions > `pl330_alloc_chan_resources' and `pl330_free_chan_resources'. This avoids > the double-lock by acquiring a different lock than `dma_pl330_rqcb'. > > NOTE that, as a result, `pl330_free_chan_resources' executes > `list_splice_tail_init' on `pch->work_list' under lock `pl330->lock', > whereas in the rest of the code `pch->work_list' is protected by > `pch->lock'. I don't know if this may cause race conditions. Similarly > `pch->cyclic' is written by `pl330_alloc_chan_resources' under > `pl330->lock' but read by `pl330_tx_submit' under `pch->lock'. > > Second, I have removed locking from `pl330_request_channel' and > `pl330_release_channel' functions. Function `pl330_request_channel' is > only called from `pl330_alloc_chan_resources', so the lock is already > held. Function `pl330_release_channel' is called from > `pl330_free_chan_resources', which already holds the lock, and from > `pl330_del'. Function `pl330_del' is called in an error path of > `pl330_probe' and at the end of `pl330_remove', but I assume that there > cannot be concurrent accesses to the protected data at those points. Applied, thanks -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
