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SubjectRe: [PATCH] DMA: PL330: Fix racy mutex unlock
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On Wed, 2012-06-13 at 15:07 +0100, Javi Merino wrote:
> pl330_update() stores a pointer to the thrd->req that finished, which
> contains a pointer to the corresponding pl330_req. This is done with
> the pl330_lock held. Then, it iterates through the req_done list,
> calling the callback for each of the requests that are done. The
> problem is that the driver releases the lock before calling the
> callback for each of the callbacks. pl330_submit_req() running in
> another processor can then acquire the lock and insert another request
> in one of the thrd->req that hasn't been processed yet, replacing the
> pointer to pl330_req there. When the callback returns in
> pl330_update() and the next rqdone is popped from the list, it
> dereferences the pl330_req pointer to the just scheduled pl330_req,
> instead of the one that has finished, calling pl330 with the wrong r.
>
> This patch fixes this by storing the pointer to pl330_req directly in
> the list.
>
> Signed-off-by: Javi Merino <javi.merino@arm.com>
> Cc: Jassi Brar <jaswinder.singh@linaro.org>
Applied, thanks

> ---
> drivers/dma/pl330.c | 26 ++++++++++----------------
> 1 files changed, 10 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index cbcc28e..b1d93b0 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -392,6 +392,8 @@ struct pl330_req {
> struct pl330_reqcfg *cfg;
> /* Pointer to first xfer in the request. */
> struct pl330_xfer *x;
> + /* Hook to attach to DMAC's list of reqs with due callback */
> + struct list_head rqd;
> };
>
> /*
> @@ -461,8 +463,6 @@ struct _pl330_req {
> /* Number of bytes taken to setup MC for the req */
> u32 mc_len;
> struct pl330_req *r;
> - /* Hook to attach to DMAC's list of reqs with due callback */
> - struct list_head rqd;
> };
>
> /* ToBeDone for tasklet */
> @@ -1683,7 +1683,7 @@ static void pl330_dotask(unsigned long data)
> /* Returns 1 if state was updated, 0 otherwise */
> static int pl330_update(const struct pl330_info *pi)
> {
> - struct _pl330_req *rqdone;
> + struct pl330_req *rqdone, *tmp;
> struct pl330_dmac *pl330;
> unsigned long flags;
> void __iomem *regs;
> @@ -1750,7 +1750,10 @@ static int pl330_update(const struct pl330_info *pi)
> if (active == -1) /* Aborted */
> continue;
>
> - rqdone = &thrd->req[active];
> + /* Detach the req */
> + rqdone = thrd->req[active].r;
> + thrd->req[active].r = NULL;
> +
> mark_free(thrd, active);
>
> /* Get going again ASAP */
> @@ -1762,20 +1765,11 @@ static int pl330_update(const struct pl330_info *pi)
> }
>
> /* Now that we are in no hurry, do the callbacks */
> - while (!list_empty(&pl330->req_done)) {
> - struct pl330_req *r;
> -
> - rqdone = container_of(pl330->req_done.next,
> - struct _pl330_req, rqd);
> -
> - list_del_init(&rqdone->rqd);
> -
> - /* Detach the req */
> - r = rqdone->r;
> - rqdone->r = NULL;
> + list_for_each_entry_safe(rqdone, tmp, &pl330->req_done, rqd) {
> + list_del(&rqdone->rqd);
>
> spin_unlock_irqrestore(&pl330->lock, flags);
> - _callback(r, PL330_ERR_NONE);
> + _callback(rqdone, PL330_ERR_NONE);
> spin_lock_irqsave(&pl330->lock, flags);
> }
>


--
~Vinod



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