Re: [PATCH v2 5/6] serial: sb1250-duart: Switch to spinlock protection for shared resource

[Philippe Mathieu-Daudé]

On 25/5/26 01:12, Maciej W. Rozycki wrote:
> The control register block is shared between DUART channels and so its
> resource has to be requested by the first channel claimed and released
> by the last one dropped.
>
> It is currently handled with an atomic counter, which however does not
> protect against a situation where request_mem_region() has failed, but
> another CPU has seen the map guard nonzero and refrained from calling
> this function for another channel where it should have (and likely also
> fail).  This parallel execution scenario can in principle be arranged
> via the TIOCSSERIAL ioctl.
>
> Switch to using an ordinary counter then and spinlock protection for the
> counter updates along with the corresponding resource request/release
> calls, so that the case described above is covered.
>
> Fixes: b45d52797432 ("sb1250-duart.c: SB1250 DUART serial support")
> Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx>
> ---
> New change in v2.
> ---
>   drivers/tty/serial/sb1250-duart.c |   28 ++++++++++++++++++----------
>   1 file changed, 18 insertions(+), 10 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxxxxxxxx>