linux-kernel - Re: [PATCH v3] mwifiex: fix sleep in atomic context bugs caused by dev

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Date:   Mon, 23 May 2022 09:20:28 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Duoming Zhou <duoming@....edu.cn>
Cc:     linux-wireless@...r.kernel.org, amitkarwar@...il.com,
        ganapathi017@...il.com, sharvari.harisangam@....com,
        huxinming820@...il.com, kvalo@...nel.org, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, rafael@...nel.org
Subject: Re: [PATCH v3] mwifiex: fix sleep in atomic context bugs caused by
 dev_coredumpv

Duoming Zhou <duoming@....edu.cn> writes:

> There are sleep in atomic context bugs when uploading device dump
> data in mwifiex. The root cause is that dev_coredumpv could not
> be used in atomic contexts, because it calls dev_set_name which
> include operations that may sleep. The call tree shows execution
> paths that could lead to bugs:
>
>    (Interrupt context)
> fw_dump_timer_fn
>   mwifiex_upload_device_dump
>     dev_coredumpv(..., GFP_KERNEL)
>       dev_coredumpm()
>         kzalloc(sizeof(*devcd), gfp); //may sleep
>         dev_set_name
>           kobject_set_name_vargs
>             kvasprintf_const(GFP_KERNEL, ...); //may sleep
>             kstrdup(s, GFP_KERNEL); //may sleep
>
> In order to let dev_coredumpv support atomic contexts, this patch
> changes the gfp_t parameter of kvasprintf_const and kstrdup in
> kobject_set_name_vargs from GFP_KERNEL to GFP_ATOMIC. What's more,
> In order to mitigate bug, this patch changes the gfp_t parameter
> of dev_coredumpv from GFP_KERNEL to GFP_ATOMIC.

vmalloc in atomic context?

Not only does dev_coredumpm set a device name dev_coredumpm creates an
entire device to hold the device dump.

My sense is that either dev_coredumpm needs to be rebuilt on a
completely different principle that does not need a device to hold the
coredump (so that it can be called from interrupt context) or that
dev_coredumpm should never be called in an context that can not sleep.

Looking at fw_dump_timer_fn the only purpose of the timer is to trigger
a device dump after a certain amount of time.  So I suspect all that is
needed to fix this issue is to change the type of devdump_timer to
struct delayed_work and use scheduled_delayed_work instead of mod_timer.

Eric

p.s.  I looked at this because there was coredump in the infrastructure
name, and I do some of the work to keep coredumps working.  Device dump
seems like a much better term, and I wished the designer of the api had
used that instead.