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

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Message-ID: <9680600d-0bea-4339-bbf5-0ccc50d13551@wanadoo.fr>
Date: Mon, 23 Sep 2024 18:47:46 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
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

Le 23/09/2024 à 18:43, Andrey Skvortsov a écrit :
> On 24-09-24 01:07, Sergey Senozhatsky wrote:
>> 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;
>>          }
> Sorry, I've seen you comment after I've sent v2. I'll do this in v3.
> 

Hi,

maybe kfree_const() to catch potential future cases and simplify code?

CJ