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

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Message-ID: <20240923154738.GE38742@google.com>
Date: Tue, 24 Sep 2024 00:47:38 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Andrey Skvortsov <andrej.skvortzov@...il.com>,
	Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
Cc: 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,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] zram: don't free statically defined names

** Re-sending properly, somehow I managed to badly mess up
   the headers the first time, sorry ***


On (24/09/24 00:34), Sergey Senozhatsky wrote:
> On (24/09/23 11:02), Andrey Skvortsov wrote:
> >     for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
> > -           kfree(zram->comp_algs[prio]);
> > +           /* Do not free statically defined compression algorithms */
>
> We probably don't really need this comment.
>
> > +           if (zram->comp_algs[prio] != default_compressor)
> > +                   kfree(zram->comp_algs[prio]);
> >             zram->comp_algs[prio] = NULL;
> >     }
>
> OK, so... I wonder how do you get a `default_compressor` on a
> non-ZRAM_PRIMARY_COMP prio.  May I ask what's your reproducer?
>
> I didn't expect `default_compressor` on ZRAM_SECONDARY_COMP
> and below.  As far as I can tell, we only do this:
>
>       comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
>
> in zram_reset_device() and zram_add().  So, how does it end up in
> ZRAM_SECONDARY_COMP...

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.

Can you please send v2 (with the feedback resolved).