linux-kernel - Re: [PATCH 2/8] radix-tree: Use local

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Message-ID: <20200519204545.GA16070@bombadil.infradead.org>
Date:   Tue, 19 May 2020 13:45:45 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/8] radix-tree: Use local_lock for protection

On Tue, May 19, 2020 at 10:19:06PM +0200, Sebastian Andrzej Siewior wrote:
> The radix-tree and idr preload mechanisms use preempt_disable() to protect
> the complete operation between xxx_preload() and xxx_preload_end().
> 
> As the code inside the preempt disabled section acquires regular spinlocks,
> which are converted to 'sleeping' spinlocks on a PREEMPT_RT kernel and
> eventually calls into a memory allocator, this conflicts with the RT
> semantics.
> 
> Convert it to a local_lock which allows RT kernels to substitute them with
> a real per CPU lock. On non RT kernels this maps to preempt_disable() as
> before, but provides also lockdep coverage of the critical region.
> No functional change.

I don't seem to have a locallock.h in my tree.  Where can I find more
information about it?

> +++ b/lib/radix-tree.c
> @@ -20,6 +20,7 @@
>  #include <linux/kernel.h>
>  #include <linux/kmemleak.h>
>  #include <linux/percpu.h>
> +#include <linux/locallock.h>
>  #include <linux/preempt.h>		/* in_interrupt() */
>  #include <linux/radix-tree.h>
>  #include <linux/rcupdate.h>