linux-kernel - Re: [PATCHv4 01/17] zram: switch to non-atomic entry locking

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Message-ID: <aytjrf5gxj24aharhcseknz65sivyhzsjcbutqbmco4wqpu36v@htnkuyarkora>
Date: Mon, 3 Feb 2025 16:33:45 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 01/17] zram: switch to non-atomic entry locking

On (25/02/03 16:11), Sergey Senozhatsky wrote:
> I guess where we actually need zram entry lock is writeback and
> recompression.  Writeback moves object from zsmalloc pool to actual
> physical storage, freeing zsmalloc memory after that and setting
> zram entry[index] handle to the backikng device's block idx, which
> needs synchronization.  Recompression does a similar thing, it frees
> the old zsmalloc handle and stores recompressed objects under new
> zsmalloc handle, it thus updates zram entry[index] handle to point
> to the new location, which needs to be synchronized.

... Luckily there is a trivial solution

---

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 402b7b175863..dd7c5ae91cc0 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 config ZRAM
        tristate "Compressed RAM block device support"
-       depends on BLOCK && SYSFS && MMU
+       depends on BLOCK && SYSFS && MMU && !PREEMPT
        select ZSMALLOC
        help
          Creates virtual block devices called /dev/zramX (X = 0, 1, ...).