Uninitialized variable in bfad_im_bsg_els_ct_request

From	Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Newsgroups	linux.kernel
Subject	Uninitialized variable in bfad_im_bsg_els_ct_request
Date	2016-12-18 21:50 +0100
Message-ID	<sPQz7-6FT-3@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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Hello,

Currently on Linus master tree and in linux-next [1],
bfad_im_bsg_els_ct_request() code starts with the following code:

int
bfad_im_bsg_els_ct_request(struct bsg_job *job)
{
	/*...*/
	struct fc_bsg_request *bsg_request = bsg_request;
	struct fc_bsg_reply *bsg_reply = job->reply;
	uint32_t command_type = bsg_request->msgcode;

The local variable "bsg_request" is initialized to itself (which would
usually mean it is uninitialized) but it is dereferenced in order to get
its "msgcode" field. As I am quite new to the kernel code and
dereferencing self-initialized local variables looks black magic to me,
could you please describe why this code is valid?

It has recently been introduced by commit 01e0e15c8b3b ("scsi: don't use
fc_bsg_job::request and fc_bsg_job::reply directly").

Thanks,
Nicolas Iooss

[1]
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/drivers/scsi/bfa/bfad_bsg.c?id=06548160dfecd1983ffd9d6795242a5cda095da5#n3356

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Uninitialized variable in bfad_im_bsg_els_ct_request Nicolas Iooss <nicolas.iooss_linux@m4x.org> - 2016-12-18 21:50 +0100

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