Re: [PATCH 02/16] scsi: atari_scsi: fix sleep_on race

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Hello Arnd,
On Thursday 27 February 2014, Michael Schmitz wrote:
Arnd Bergmann wrote:
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?)

Sorry about messing it up again. I though I had fixed it up the
way you commented when you said it worked.
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.

I definitely trust you to have the right version, since you did the
testing.

I'm glad I double checked, since there's one other error left in my correction to your patch below:

The in_irq() condition is not sufficient, we need in_interrupt() there. This has somehow slipped into a related patch sent to linux-scsi, so I'll have to refactor the lot. Bugger.

I'll resend the correct version via Geert.

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())

Yes, by inspection your version looks correct and mine looks wrong.
I had figured this out before, just sent the wrong version.

These things happen if you bother fixing other people's weird code :-)
And as I mentioned above, I missed another detail myself

@@ -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));
                }

I did correct this part compared to my first patch, but forgot
to change the other hunk.

Can you send your version of the patch to Geert for inclusion?
That way I don't have the danger of missing another negation.
This code is clearly too weird to rely on inspection alone and
we know that your version was working when you last tested it.

Will do - I'll CC: you in so you can ACK the patch if Geert needs convincing.

Cheers,

   Michael

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