linux-kernel - Re: [PATCH] nvme: fix uninitialized-variable warning

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Date:   Fri, 14 Feb 2020 04:51:06 +0900
From:   Keith Busch <kbusch@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Oleksandr Natalenko <oleksandr@...hat.com>,
        Bart Van Assche <bvanassche@....org>,
        Chaitanya Kulkarni <chaitanya.kulkarni@....com>,
        Marta Rybczynska <mrybczyn@...ray.eu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-nvme@...ts.infradead.org, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH] nvme: fix uninitialized-variable warning

On Thu, Jan 30, 2020 at 07:48:15AM -0800, Christoph Hellwig wrote:
> On Thu, Jan 30, 2020 at 04:36:48PM +0100, Arnd Bergmann wrote:
> > > This one is just gross.  I think we'll need to find some other fix
> > > that doesn't obsfucate the code as much.
> > 
> > Initializing the nvme_result in nvme_features() would do it, as would
> > setting it in the error path in __nvme_submit_sync_cmd() -- either
> > way the compiler cannot be confused about whether it is initialized
> > later on.
> 
> Given that this is outside the hot path we can just zero the whole
> structure before submitting the I/O.

I think this should be okay:

---
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 7f05deada7f4..4aeed750dab2 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1165,8 +1165,8 @@ static int nvme_identify_ns(struct nvme_ctrl *ctrl,
 static int nvme_features(struct nvme_ctrl *dev, u8 op, unsigned int fid,
 		unsigned int dword11, void *buffer, size_t buflen, u32 *result)
 {
+	union nvme_result res = { 0 };
 	struct nvme_command c;
-	union nvme_result res;
 	int ret;
 
 	memset(&c, 0, sizeof(c));
--