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    SubjectRe: [PATCH] dmaengine: pl330: fix double lock
    On Wed, Jan 11, 2017 at 02:00:21PM +0100, iari@itu.dk wrote:
    > From: Iago Abal <mail@iagoabal.eu>
    >
    > 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

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