Hi,
On Thu, Jun 24, 2021 at 08:49:36PM +0200, Christophe JAILLET wrote:
> The intent here is to return an error code if we don't find what we are
> looking for in the 'list_for_each_entry()' loop.
>
> 's' is not NULL if the list is empty or if we scan the complete list.
> Introduce a new 'found' variable to handle such cases.
>
> Fixes: 60dd49298ec5 ("ALSA: firewire-lib: handle several AMDTP streams in callback handler of IRQ target")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> ---
> We could test with" if (list_entry_is_head(s, &d->streams, list))"
> instead, but I find it much less readable.
> ---
> sound/firewire/amdtp-stream.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
> index aad9778d1c4d..9be2260e4ca2 100644
> --- a/sound/firewire/amdtp-stream.c
> +++ b/sound/firewire/amdtp-stream.c
> @@ -1943,6 +1943,7 @@ int amdtp_domain_start(struct amdtp_domain *d, unsigned int tx_init_skip_cycles,
> unsigned int events_per_period = d->events_per_period;
> unsigned int queue_size;
> struct amdtp_stream *s;
> + bool found = false;
> int err;
>
> if (replay_seq) {
> @@ -1955,10 +1956,12 @@ int amdtp_domain_start(struct amdtp_domain *d, unsigned int tx_init_skip_cycles,
>
> // Select an IT context as IRQ target.
> list_for_each_entry(s, &d->streams, list) {
> - if (s->direction == AMDTP_OUT_STREAM)
> + if (s->direction == AMDTP_OUT_STREAM) {
> + found = true;
> break;
> + }
> }
> - if (!s)
> + if (!found)
> return -ENXIO;
> d->irq_target = s;
>
> --
> 2.30.2
Indeed. Nice to catch it. The bug affects Linux kernel v5.5 or later.
Acked-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
In kernel v5.10 or later, we can use 'list_entry_is_head()' macro added
by a commit e130816164e2 ("include/linux/list.h: add a macro to test if
entry is pointing to the head"). However the development of ALSA firewire
stack is out-of-tree repository for my convenience to backport it to kernel
v4.17 or later (I need testers...), so I prefer your change.
Thanks
Takashi Sakamoto
