From: Kalle Valo <kvalo@kernel.org>
To: duoming@zju.edu.cn
Cc: "Jeff Johnson" <quic_jjohnson@quicinc.com>,
linux-kernel@vger.kernel.org, amitkarwar@gmail.com,
ganapathi017@gmail.com, sharvari.harisangam@nxp.com,
huxinming820@gmail.com, davem@davemloft.net, edumazet@google.com,
kuba@kernel.org, pabeni@redhat.com,
linux-wireless@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH net v2] net: wireless: marvell: mwifiex: fix sleep in atomic context bugs
Date: Sat, 21 May 2022 09:32:37 +0300 [thread overview]
Message-ID: <87ilpzwg3e.fsf@kernel.org> (raw)
In-Reply-To: <ed03525.253c1.180e4a21950.Coremail.duoming@zju.edu.cn> (duoming's message of "Sat, 21 May 2022 11:21:10 +0800 (GMT+08:00)")
duoming@zju.edu.cn writes:
> Hello,
>
> On Fri, 20 May 2022 09:08:52 -0700 Jeff Johnson wrote:
>
>> >>>>> There are sleep in atomic context bugs when uploading device dump
>> >>>>> data on usb interface. The root cause is that the operations that
>> >>>>> may sleep are called in fw_dump_timer_fn which is a timer handler.
>> >>>>> The call tree shows the execution paths that could lead to bugs:
>> >>>>>
>> >>>>> (Interrupt context)
>> >>>>> fw_dump_timer_fn
>> >>>>> mwifiex_upload_device_dump
>> >>>>> dev_coredumpv(..., GFP_KERNEL)
>> >>
>> >> just looking at this description, why isn't the simple fix just to
>> >> change this call to use GFP_ATOMIC?
>> >
>> > Because change the parameter of dev_coredumpv() to GFP_ATOMIC could only solve
>> > partial problem. The following GFP_KERNEL parameters are in /lib/kobject.c
>> > which is not influenced by dev_coredumpv().
>> >
>> > kobject_set_name_vargs
>> > kvasprintf_const(GFP_KERNEL, ...); //may sleep
>> > kstrdup(s, GFP_KERNEL); //may sleep
>>
>> Then it seems there is a problem with dev_coredumpm().
>>
>> dev_coredumpm() takes a gfp param which means it expects to be called in
>> any context, but it then calls dev_set_name() which, as you point out,
>> cannot be called from an atomic context.
>>
>> So if we cannot change the fact that dev_set_name() cannot be called
>> from an atomic context, then it would seem to follow that
>> dev_coredumpv also cannot be called from an atomic
>> context and hence their gfp param is pointless and should presumably be
>> removed.
>
> Thanks for your time and suggestions! I think the gfp_t parameter of dev_coredumpv and
> dev_coredumpm may not be removed, because it could be used to pass value to gfp_t
> parameter of kzalloc in dev_coredumpm. What's more, there are also many other places
> use dev_coredumpv and dev_coredumpm, if we remove the gfp_t parameter, there are too many
> places that need to modify and these places are not in interrupt
> context.
"Too many users" is not a valid reason to leave a bug in place, either
dev_coredumpv() should support GFP_ATOMIC or the gfp_t parameter should
be removed.
> There are two solutions now: one is to moves the operations that may
> sleep into a work item.
That does not fix the root cause that dev_coredumpv() claims it can be
called in atomic contexts.
> Another is to change the gfp_t parameter of dev_coredumpv from GFP_KERNEL to GFP_ATOMIC, and
> change the gfp_t parameter of kvasprintf_const and kstrdup from GFP_KERNEL to
> "in_interrupt() ? GFP_ATOMIC : GFP_KERNEL".
in_interrupt() is deprecated and should not be used. And I don't think
it detects all atomic contexts like spinlocks.
--
https://patchwork.kernel.org/project/linux-wireless/list/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
next prev parent reply other threads:[~2022-05-21 6:32 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-19 13:53 [PATCH net v2] net: wireless: marvell: mwifiex: fix sleep in atomic context bugs Duoming Zhou
2022-05-19 14:58 ` Kalle Valo
2022-05-19 15:14 ` duoming
2022-05-19 15:48 ` Jeff Johnson
2022-05-20 0:08 ` duoming
2022-05-20 16:08 ` Jeff Johnson
2022-05-21 3:21 ` duoming
2022-05-21 6:32 ` Kalle Valo [this message]
2022-05-21 13:59 ` duoming
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