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SubjectRe: [PATCH 02/16] scsi: atari_scsi: fix sleep_on race
Arnd Bergmann wrote:
> 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: Michael Schmitz <schmitzmic@gmail.com>
> 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..b33ce34 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(),
> + local_irq_restore(flags),
> + local_irq_save(flags));
>
> while (!falcon_got_lock) {
> if (in_irq())
> @@ -562,7 +565,10 @@ static void falcon_get_lock(void)
> falcon_trying_lock = 0;
> wake_up(&falcon_try_wait);
> } else {
> - sleep_on(&falcon_try_wait);
> + wait_event_cmd(falcon_try_wait,
> + falcon_got_lock && !falcon_trying_lock,
> + local_irq_restore(flags),
> + local_irq_save(flags));
> }
> }
>
>
Nack - the completion condition in the first hunk has its logic
reversed. Try this instead (while() loops while condition true, do {}
until () loops while condition false, no?)

I'm 99% confident I had tested your current version of the patch before
and found it still attempts to schedule while in interrupt. I can retest
if you prefer, but that'll have to wait a few days.

diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c
index a3e6c8a..cc1b013 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(),
+ local_irq_restore(flags),
+ local_irq_save(flags));

while (!falcon_got_lock) {
if (in_irq())
@@ -562,7 +565,10 @@ static void falcon_get_lock(void)
falcon_trying_lock = 0;
wake_up(&falcon_try_wait);
} else {
- sleep_on(&falcon_try_wait);
+ wait_event_cmd(falcon_try_wait,
+ falcon_got_lock && !falcon_trying_lock,
+ local_irq_restore(flags),
+ local_irq_save(flags));
}
}

Cheers,

Michael



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