Em 20-09-2011 07:32, Doron Cohen escreveu:
> Hi,
> This patch step is a Bug fix - avoid (rare) dead locks causing the
> driver to hang when module removed.
> Thanks,
> Doron Cohen
>
> -----------------------
>
>>From ad75d9ce48d440c6db6c5147530f1e23de2fcb28 Mon Sep 17 00:00:00 2001
> From: Doron Cohen <[email protected]>
> Date: Tue, 20 Sep 2011 08:46:52 +0300
> Subject: [PATCH 19/21] Bug fix - waiting for free buffers might have
> caused dead locks. Mechanism changed so locks are released around each
> wait.
>
> ---
> drivers/media/dvb/siano/smscoreapi.c | 53
> +++++++++++++++++++++++++++------
> 1 files changed, 43 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/media/dvb/siano/smscoreapi.c
> b/drivers/media/dvb/siano/smscoreapi.c
> index bb92351..0555a38 100644
> --- a/drivers/media/dvb/siano/smscoreapi.c
> +++ b/drivers/media/dvb/siano/smscoreapi.c
> @@ -1543,26 +1543,59 @@ EXPORT_SYMBOL_GPL(smscore_onresponse);
> *
> * @return pointer to descriptor on success, NULL on error.
> */
> -
> -struct smscore_buffer_t *get_entry(struct smscore_device_t *coredev)
> +struct smscore_buffer_t *smscore_getbuffer(struct smscore_device_t
> *coredev)
> {
> struct smscore_buffer_t *cb = NULL;
> unsigned long flags;
>
> + DEFINE_WAIT(wait);
> +
> + spin_lock_irqsave(&coredev->bufferslock, flags);
> +
> + /* set the current process state to interruptible sleep
> + * in case schedule() will be called, this process will go to sleep
> + * and woken up only when a new buffer is available (see
> smscore_putbuffer)
> + */
> + prepare_to_wait(&coredev->buffer_mng_waitq, &wait,
> TASK_INTERRUPTIBLE);
> +
> + if (list_empty(&coredev->buffers)) {
> + sms_debug("no avaliable common buffer, need to schedule");
> +
> + /*
> + * before going to sleep, release the lock
> + */
> + spin_unlock_irqrestore(&coredev->bufferslock, flags);
> +
> + schedule();
> +
> + sms_debug("wake up after schedule()");
> +
> + /*
> + * acquire the lock again
> + */
> spin_lock_irqsave(&coredev->bufferslock, flags);
> - if (!list_empty(&coredev->buffers)) {
> - cb = (struct smscore_buffer_t *) coredev->buffers.next;
> - list_del(&cb->entry);
> }
The proper fix is not to call schedule(). It is to use a waitqueue. The
current driver has it already. I think you're likely reverting the fix here.
Please take a look at the git history to see how it was solved.
> +
> + /*
> + * in case that schedule() was skipped, set the process state
> to running
> + */
> + finish_wait(&coredev->buffer_mng_waitq, &wait);
> +
> + /*
> + * verify that the list is not empty, since it might have been
> + * emptied during the sleep
> + * comment : this sitation can be avoided using
> spin_unlock_irqrestore_exclusive
> + */
> + if (list_empty(&coredev->buffers)) {
> + sms_err("failed to allocate buffer, returning NULL");
> spin_unlock_irqrestore(&coredev->bufferslock, flags);
> - return cb;
> + return NULL;
> }
>
> -struct smscore_buffer_t *smscore_getbuffer(struct smscore_device_t
> *coredev)
> -{
> - struct smscore_buffer_t *cb = NULL;
> + cb = (struct smscore_buffer_t *) coredev->buffers.next;
> + list_del(&cb->entry);
>
> - wait_event(coredev->buffer_mng_waitq, (cb = get_entry(coredev)));
> + spin_unlock_irqrestore(&coredev->bufferslock, flags);
>
> return cb;
> }
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