linux-kernel - Re: [PATCH] zram: Replace bit spinlocks with spinlock_t for PREEMPT

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Date: Wed, 19 Jun 2024 11:34:23 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Mike Galbraith <umgwanakikbuti@...il.com>,
 Minchan Kim <minchan@...nel.org>,
 Sergey Senozhatsky <senozhatsky@...omium.org>,
 Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] zram: Replace bit spinlocks with spinlock_t for
 PREEMPT_RT.

On 6/19/24 9:08 AM, Sebastian Andrzej Siewior wrote:
> From: Mike Galbraith <umgwanakikbuti@...il.com>
> 
> The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping
> lock on PREEMPT_RT and it can not be acquired in this context. In this locked
> section, zs_free() acquires a zs_pool::lock, and there is access to
> zram::wb_limit_lock.
> 
> Use a spinlock_t on PREEMPT_RT for locking and set/ clear ZRAM_LOCK bit after
> the lock has been acquired/ dropped.

The conditional code depending on CONFIG_PREEMPT_RT is nasty. Why not
just get rid of that and use the CONFIG_PREEMPT_RT variants for
everything? They are either good enough to work well in general, or it
should be redone such that it is.

-- 
Jens Axboe