Re: [PATCH, RFC 02/30] scsi: atari_scsi: fix sleep_on race

schmitz
2014-01-13T08:21:00Z

Arnd,
>
> I'll debug this a bit to see where it gets stuck. Thanks for looking
> into this ugly mess of code!
>
> Cheers,
>
> Michael
>
>
>
> Michael Schmitz wrote:
>> Geert,
>>
>> thanks for passing that on - I had in fact disabled that feature of
>> the driver for a good part of the 3.x series of kernels while
>> attempting to figure out what else is wrong with the locking scheme.
>>
>> I'll take a fresh stab at this.
>>
>> Cheers,
>>
>> Michael
>>
>>
>> Am 03.01.2014 um 01:26 schrieb Geert Uytterhoeven:
>>
>>> ---------- Forwarded message ----------
>>> From: Arnd Bergmann <arnd@arndb.de>
>>> Date: Thu, Jan 2, 2014 at 1:07 PM
>>> Subject: [PATCH, RFC 02/30] scsi: atari_scsi: fix sleep_on race
>>> To: linux-kernel@vger.kernel.org
>>> Cc: Arnd Bergmann <arnd@arndb.de>, Geert Uytterhoeven
>>> <geert@linux-m68k.org>, "James E.J. Bottomley"
>>> <JBottomley@parallels.com>, linux-scsi@vger.kernel.org
>>>
>>>
>>> sleep_on is known broken and going away. The atari_scsi driver is
>>> one of
>>> two remaining users in the falcon_get_lock() function, which is a
>>> rather
>>> crazy piece of code. This does not attempt to fix the driver's locking
>>> scheme in general, but at least prevents falcon_get_lock from going to
>>> sleep when no other thread holds the same lock or tries to get it,
>>> and we no longer schedule with irqs disabled.
>>>
>>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>>> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
>>> Cc: James E.J. Bottomley <JBottomley@parallels.com>
>>> Cc: linux-scsi@vger.kernel.org
>>> ---
>>> drivers/scsi/atari_scsi.c | 12 +++++++++---
>>> 1 file changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c
>>> index a3e6c8a..b55a58a 100644
>>> --- a/drivers/scsi/atari_scsi.c
>>> +++ b/drivers/scsi/atari_scsi.c
>>> @@ -90,6 +90,7 @@
>>> #include <linux/init.h>
>>> #include <linux/nvram.h>
>>> #include <linux/bitops.h>
>>> +#include <linux/wait.h>
>>>
>>> #include <asm/setup.h>
>>> #include <asm/atarihw.h>
>>> @@ -549,8 +550,10 @@ static void falcon_get_lock(void)
>>>
>>> local_irq_save(flags);
>>>
>>> - while (!in_irq() && falcon_got_lock && stdma_others_waiting())
>>> - sleep_on(&falcon_fairness_wait);
>>> + wait_event_cmd(falcon_fairness_wait,
>>> + !in_irq() && falcon_got_lock &&
>>> stdma_others_waiting(),

Replace by:
in_irq() || !falcon_got_lock ||
!stdma_others_waiting(),

Much better now. Needs stress testing on real hardware, but that'll have
to wait until the weekend I guess.

Cheers,

Michael