linux-kernel - Re: [PATCH 1/2] Introduce write_trylock

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Message-ID: <a781481a0705092018v489b712dxa377aeb502b66fef@mail.gmail.com>
Date:	Thu, 10 May 2007 08:48:35 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Sripathi Kodi" <sripathik@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: [PATCH 1/2] Introduce write_trylock_irqsave

On 5/9/07, Sripathi Kodi <sripathik@...ibm.com> wrote:
> Hi,
>
> I am trying to fix the BUG I mentioned here:
> http://lkml.org/lkml/2007/04/20/41. I noticed that an elegant way to solve
> this problem is to have a write_trylock_irqsave helper function. Since we
> don't have this now, the code in ptrace_attach  implements it using
> local_irq_disable and write_trylock. I wish to add write_trylock_irqsave to
> mainline kernel and then fix the -rt specific problem using this.
>
> The patch below adds write_trylock_irqsave function.

Why not implement this as follows? That way we're able to (1) be
consistent in style with spin_trylock_irqsave, (2) type fewer lines,
(3) touch fewer files, and (4) not add extra bulk to kernel text size
either.

For the sake of completeness of the API, we could also add a
read_trylock_irqsave, but I'd be against the _irq variants (or should
we call them hazards) that don't save / restore.

Signed-off-by: Satyam Sharma <ssatyam@....iitk.ac.in>

---

 include/linux/spinlock.h |    7 +++++++
 1 file changed, 7 insertions(+)

---

diff -ruNp a/include/linux/spinlock.h b/include/linux/spinlock.h
--- a/include/linux/spinlock.h	2007-04-26 08:38:32.000000000 +0530
+++ b/include/linux/spinlock.h	2007-05-10 08:43:32.000000000 +0530
@@ -282,6 +282,13 @@ do {						\
 	1 : ({ local_irq_restore(flags); 0; }); \
 })

+#define write_trylock_irqsave(lock, flags) \
+({ \
+	local_irq_save(flags); \
+	write_trylock(lock) ? \
+	1 : ({ local_irq_restore(flags); 0; }); \
+})
+
 /*
  * Locks two spinlocks l1 and l2.
  * l1_first indicates if spinlock l1 should be taken first.
-
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