linux-kernel - Re: [PATCH] lib/sg_pool: change module_init(sg_pool_init) to subsys

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Message-ID: <20220923152809.GA455235@roeck-us.net>
Date:   Fri, 23 Sep 2022 08:28:09 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-kbuild@...r.kernel.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Ming Lin <ming.l@....samsung.com>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH] lib/sg_pool: change module_init(sg_pool_init) to
 subsys_initcall

On Fri, Sep 23, 2022 at 08:38:35PM +0900, Masahiro Yamada wrote:
> sg_alloc_table_chained() is called by several drivers, but if it is
> called before sg_pool_init(), it results in a NULL pointer dereference
> in sg_pool_alloc().
> 
> Since commit 9b1d6c895002 ("lib: scatterlist: move SG pool code from
> SCSI driver to lib/sg_pool.c"), we rely on module_init(sg_pool_init)
> is invoked before other module_init calls but this assumption is
> fragile.
> 
> I slightly changed the link order while Kbuild refactoring Kbuild,
> then uncovered this issue. I should keep the current link order, but
> depending on a specific call order among module_init is so fragine.
> 
> We usually define the init order by specifying *_initcall correctly,
> or delay the driver probing by returning -EPROBE_DEFER.
> 
> Change module_initcall() to subsys_initcall(), and also delete the
> pointless module_exit() because lib/sg_pool.c is always compiled as
> built-in. (CONFIG_SG_POOL is bool)
> 
> Link: https://lore.kernel.org/all/20220921043946.GA1355561@roeck-us.net/
> Link: https://lore.kernel.org/all/8e70837d-d859-dfb2-bf7f-83f8b31467bc@samsung.com/
> Fixes: 9b1d6c895002 ("lib: scatterlist: move SG pool code from SCSI driver to lib/sg_pool.c")
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter