linux-kernel - Re: [PATCH v3 7/7] zram: Use local lock to protect per-CPU data

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Message-ID: <20200529205740.GD86436@google.com>
Date:   Fri, 29 May 2020 13:57:40 -0700
From:   Minchan Kim <minchan@...nel.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>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v3 7/7] zram: Use local lock to protect per-CPU data

On Wed, May 27, 2020 at 10:11:19PM +0200, Sebastian Andrzej Siewior wrote:
> From: Mike Galbraith <umgwanakikbuti@...il.com>
> 
> The zcomp driver uses per-CPU compression. The per-CPU data pointer is
> acquired with get_cpu_ptr() which implicitly disables preemption.
> It allocates memory inside the preempt disabled region which conflicts
> with the PREEMPT_RT semantics.
> 
> Replace the implicit preemption control with an explicit local lock.
> This allows RT kernels to substitute it with a real per CPU lock, which
> serializes the access but keeps the code section preemptible. On non RT
> kernels this maps to preempt_disable() as before, i.e. no functional
> change.
> 
> [bigeasy: Use local_lock(), description, drop reordering]
> 
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Acked-by: Minchan Kim <minchan@...nel.org>