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From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] nvdimm: avoid bogus -Wmaybe-uninitialized warning
Date: Tue, 1 Aug 2017 12:00:17 -0600	[thread overview]
Message-ID: <20170801180017.GC20061@linux.intel.com> (raw)
In-Reply-To: <20170801114926.1171418-1-arnd@arndb.de>

On Tue, Aug 01, 2017 at 01:48:48PM +0200, Arnd Bergmann wrote:
> Removing the btt_rw_page/pmem_rw_page functions had a surprising
> side-effect of introducing a false-positive warning in another
> function, due to changed inlining decisions in gcc:
> 
> In file included from drivers/nvdimm/pmem.c:36:0:
> drivers/nvdimm/pmem.c: In function 'pmem_make_request':
> drivers/nvdimm/nd.h:407:2: error: 'start' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/nvdimm/pmem.c:174:16: note: 'start' was declared here
> In file included from drivers/nvdimm/btt.c:27:0:
> drivers/nvdimm/btt.c: In function 'btt_make_request':
> drivers/nvdimm/nd.h:407:2: error: 'start' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/nvdimm/btt.c:1202:16: note: 'start' was declared here
> 
> The problem is that gcc fails to track the value of the 'do_acct'
> variable here and has to read it back from stack, but it does
> remember that 'start' may be uninitialized sometimes.
> 
> This shuts up the warning by making nd_iostat_start() always
> initialize the 'start' variable. In those cases that gcc successfully
> tracks the state of the variable, this will have no effect.
> 
> Fixes: 503a5e89b1de ("drivers/nvdimm/btt.c: remove btt_rw_page()")
> Fixes: 58100d6e735e ("drivers/nvdimm/pmem.c: remove pmem_rw_page()")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

This change looks fine:

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>

I believe the patches removing the btt_rw_page() and btt_rw_page() are on hold
until I can get some performance numbers to justify them.

Dan, do you want to take this as is, or do you want me to include it in my
larger rw_page() series if/when that gets revived?
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WARNING: multiple messages have this Message-ID (diff)
From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Christoph Hellwig <hch@infradead.org>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Toshi Kani <toshi.kani@hpe.com>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] nvdimm: avoid bogus -Wmaybe-uninitialized warning
Date: Tue, 1 Aug 2017 12:00:17 -0600	[thread overview]
Message-ID: <20170801180017.GC20061@linux.intel.com> (raw)
In-Reply-To: <20170801114926.1171418-1-arnd@arndb.de>

On Tue, Aug 01, 2017 at 01:48:48PM +0200, Arnd Bergmann wrote:
> Removing the btt_rw_page/pmem_rw_page functions had a surprising
> side-effect of introducing a false-positive warning in another
> function, due to changed inlining decisions in gcc:
> 
> In file included from drivers/nvdimm/pmem.c:36:0:
> drivers/nvdimm/pmem.c: In function 'pmem_make_request':
> drivers/nvdimm/nd.h:407:2: error: 'start' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/nvdimm/pmem.c:174:16: note: 'start' was declared here
> In file included from drivers/nvdimm/btt.c:27:0:
> drivers/nvdimm/btt.c: In function 'btt_make_request':
> drivers/nvdimm/nd.h:407:2: error: 'start' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/nvdimm/btt.c:1202:16: note: 'start' was declared here
> 
> The problem is that gcc fails to track the value of the 'do_acct'
> variable here and has to read it back from stack, but it does
> remember that 'start' may be uninitialized sometimes.
> 
> This shuts up the warning by making nd_iostat_start() always
> initialize the 'start' variable. In those cases that gcc successfully
> tracks the state of the variable, this will have no effect.
> 
> Fixes: 503a5e89b1de ("drivers/nvdimm/btt.c: remove btt_rw_page()")
> Fixes: 58100d6e735e ("drivers/nvdimm/pmem.c: remove pmem_rw_page()")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

This change looks fine:

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>

I believe the patches removing the btt_rw_page() and btt_rw_page() are on hold
until I can get some performance numbers to justify them.

Dan, do you want to take this as is, or do you want me to include it in my
larger rw_page() series if/when that gets revived?

  reply	other threads:[~2017-08-01 17:58 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-01 11:48 [PATCH] nvdimm: avoid bogus -Wmaybe-uninitialized warning Arnd Bergmann
2017-08-01 11:48 ` Arnd Bergmann
2017-08-01 18:00 ` Ross Zwisler [this message]
2017-08-01 18:00   ` Ross Zwisler
2017-08-01 18:07   ` Dan Williams
2017-08-01 18:07     ` Dan Williams
2017-08-01 21:45 ` Andrew Morton
2017-08-01 21:45   ` Andrew Morton
2017-08-01 22:23   ` Ross Zwisler
2017-08-01 22:23     ` Ross Zwisler
2017-08-02 10:54     ` Arnd Bergmann
2017-08-02 10:54       ` Arnd Bergmann

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