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From: Will Deacon <will@kernel.org>
To: peterz@infradead.org
Cc: Oleg Nesterov <oleg@redhat.com>, Hou Tao <houtao1@huawei.com>,
	Ingo Molnar <mingo@redhat.com>, Dennis Zhou <dennis@kernel.org>,
	Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Jan Kara <jack@suse.cz>
Subject: Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count
Date: Tue, 15 Sep 2020 17:11:23 +0100	[thread overview]
Message-ID: <20200915161123.GC26745@willie-the-truck> (raw)
In-Reply-To: <20200915160344.GH35926@hirez.programming.kicks-ass.net>

On Tue, Sep 15, 2020 at 06:03:44PM +0200, peterz@infradead.org wrote:
> On Tue, Sep 15, 2020 at 05:51:50PM +0200, peterz@infradead.org wrote:
> 
> > Anyway, I'll rewrite the Changelog and stuff it in locking/urgent.
> 
> How's this?
> 
> ---
> Subject: locking/percpu-rwsem: Use this_cpu_{inc,dec}() for read_count
> From: Hou Tao <houtao1@huawei.com>
> Date: Tue, 15 Sep 2020 22:07:50 +0800
> 
> From: Hou Tao <houtao1@huawei.com>
> 
> The __this_cpu*() accessors are (in general) IRQ-unsafe which, given
> that percpu-rwsem is a blocking primitive, should be just fine.
> 
> However, file_end_write() is used from IRQ context and will cause
> load-store issues.

... on architectures where the per-cpu accessors are not atomic.

> 
> Fixing it by using the IRQ-safe this_cpu_*() for operations on

Fixing => Fix ?

> read_count. This will generate more expensive code on a number of
> platforms, which might cause a performance regression for some of the
> other percpu-rwsem users.
> 
> If any such is reported, we can consider alternative solutions.
> 
> Fixes: 70fe2f48152e ("aio: fix freeze protection of aio writes")
> Signed-off-by: Hou Tao <houtao1@huawei.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://lkml.kernel.org/r/20200915140750.137881-1-houtao1@huawei.com
> ---
>  include/linux/percpu-rwsem.h  |    8 ++++----
>  kernel/locking/percpu-rwsem.c |    4 ++--
>  2 files changed, 6 insertions(+), 6 deletions(-)

For the patch:

Acked-by: Will Deacon <will@kernel.org>

Will

  reply	other threads:[~2020-09-15 22:31 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 14:07 Hou Tao
2020-09-15 15:06 ` peterz
2020-09-15 15:31   ` Oleg Nesterov
2020-09-15 15:51     ` peterz
2020-09-15 16:03       ` peterz
2020-09-15 16:11         ` Will Deacon [this message]
2020-09-15 18:11           ` peterz
2020-09-16  8:20             ` Will Deacon
2020-09-15 16:47         ` Oleg Nesterov
2020-09-16 12:32         ` Hou Tao
2020-09-16 12:51           ` peterz
2020-09-17  8:48           ` Will Deacon
2020-09-24 11:55             ` Hou Tao
2020-09-29 17:49               ` Will Deacon
2020-09-29 18:07                 ` Ard Biesheuvel
2020-09-17 10:51           ` Boaz Harrosh
2020-09-17 12:01             ` Oleg Nesterov
2020-09-17 12:48               ` Matthew Wilcox
2020-09-17 13:22                 ` peterz
2020-09-17 13:34                 ` Oleg Nesterov
2020-09-17 13:46                 ` Boaz Harrosh
2020-09-17 14:46                   ` Christoph Hellwig
2020-09-18  9:07               ` Jan Kara
2020-09-18 10:01                 ` peterz
2020-09-18 10:04                   ` peterz
2020-09-18 10:07                     ` peterz
2020-09-18 10:12                   ` peterz
2020-09-18 10:48                     ` Oleg Nesterov
2020-09-18 11:03                       ` peterz
2020-09-18 13:09                         ` Oleg Nesterov
2020-09-18 13:26                           ` Jan Kara
2020-09-20 23:49                             ` Dave Chinner

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