linux-kernel - Re: [PATCH v2] futex: fix a race condition between REQUEUE

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Date:	Sun, 26 Oct 2014 16:04:53 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Brian Silverman <bsilver16384@...il.com>
cc:	austin.linux@...il.com, linux-kernel@...r.kernel.org,
	darren@...art.com, peterz@...radead.org
Subject: Re: [PATCH v2] futex: fix a race condition between REQUEUE_PI and
 task death

On Sat, 25 Oct 2014, Brian Silverman wrote:
> @@ -64,6 +64,7 @@
>  #include <linux/hugetlb.h>
>  #include <linux/freezer.h>
>  #include <linux/bootmem.h>
> +#include <linux/lockdep.h>

Already included.
  
>   * PI futexes can not be requeued and must remove themself from the
>   * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
>   * and dropped here.
> + * Must be called with the hb lock held.

It's already required that the hb lock, i.e. q->lock_ptr is held on
entry. So there is no point for adding hb to the interface. We rather
add "struct spin_lock *lock" to free_pi_state() and hand in
q->lock_ptr from here and &hb2->lock from requeue_pi.

I take the immediate bugfix and strip out this debug stuff for
now. Care to resend this part?

Thanks,

	tglx
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