linux-kernel - Re: [PATCH] zram: don't free statically defined names

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Message-ID: <20240923160708.GF38742@google.com>
Date: Tue, 24 Sep 2024 01:07:08 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Andrey Skvortsov <andrej.skvortzov@...il.com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>,
	Minchan Kim <minchan@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] zram: don't free statically defined names

On (24/09/23 18:55), Andrey Skvortsov wrote:
[..]
> > Ugh, I know what's happening.  You don't have CONFIG_ZRAM_MULTI_COMP
> > so that ZRAM_PRIMARY_COMP and ZRAM_SECONDARY_COMP are the same thing.
> > Yeah, that all makes sense now, I haven't thought about it.
> 
> yes, I don't have CONFIG_ZRAM_MULTI_COMP set. I'll include your
> comment into commit description for v2.

Thanks.

Can you do it something like the diff below?  Let's iterate
->comp_algs from ZRAM_PRIMARY_COMP.  I don't really mind the
"Do not free statically defined" comment, up to you.

And the commit message probably can stay that: on !CONFIG_ZRAM_MULTI_COMP
systems ZRAM_SECONDARY_COMP can hold default_compressor, because it's
the same offset as ZRAM_PRIMARY_COMP, so we need to make sure that we
don't attempt to kfree() the statically defined comp name.

---

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index c3d245617083..ad9c9bc3ccfc 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -2115,8 +2115,10 @@ static void zram_destroy_comps(struct zram *zram)
                zram->num_active_comps--;
        }
 
-       for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
-               kfree(zram->comp_algs[prio]);
+       for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
+               /* Do not free statically defined compression algorithms */
+               if (zram->comp_algs[prio] != default_compressor)
+                       kfree(zram->comp_algs[prio]);
                zram->comp_algs[prio] = NULL;
        }