Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[kernel test robot]

Hi Dominique,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 8f5ae30d69d7543eee0d70083daf4de8fe15d585]

url:    https://github.com/intel-lab-lkp/linux/commits/Dominique-Martinet-via-B4-Relay/iov_iter-iterate_folioq-fix-handling-of-offset-folio-size/20250811-154319
base:   8f5ae30d69d7543eee0d70083daf4de8fe15d585
patch link:    https://lore.kernel.org/r/20250811-iot_iter_folio-v1-1-d9c223adf93c%40codewreck.org
patch subject: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size
config: i386-buildonly-randconfig-002-20250811 (https://download.01.org/0day-ci/archive/20250812/202508120250.Eooq2ydr-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250812/202508120250.Eooq2ydr-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202508120250.Eooq2ydr-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from lib/iov_iter.c:14:
>> include/linux/iov_iter.h:171:7: warning: variable 'remain' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
     171 |                 if (skip >= fsize)
         |                     ^~~~~~~~~~~~~
   include/linux/iov_iter.h:190:7: note: uninitialized use occurs here
     190 |                 if (remain)
         |                     ^~~~~~
   include/linux/iov_iter.h:171:3: note: remove the 'if' if its condition is always false
     171 |                 if (skip >= fsize)
         |                 ^~~~~~~~~~~~~~~~~~
     172 |                         goto next;
         |                         ~~~~~~~~~
   include/linux/iov_iter.h:163:22: note: initialize the variable 'remain' to silence this warning
     163 |                 size_t part, remain, consumed;
         |                                    ^
         |                                     = 0
   1 warning generated.


vim +171 include/linux/iov_iter.h

   143	
   144	/*
   145	 * Handle ITER_FOLIOQ.
   146	 */
   147	static __always_inline
   148	size_t iterate_folioq(struct iov_iter *iter, size_t len, void *priv, void *priv2,
   149			      iov_step_f step)
   150	{
   151		const struct folio_queue *folioq = iter->folioq;
   152		unsigned int slot = iter->folioq_slot;
   153		size_t progress = 0, skip = iter->iov_offset;
   154	
   155		if (slot == folioq_nr_slots(folioq)) {
   156			/* The iterator may have been extended. */
   157			folioq = folioq->next;
   158			slot = 0;
   159		}
   160	
   161		do {
   162			struct folio *folio = folioq_folio(folioq, slot);
   163			size_t part, remain, consumed;
   164			size_t fsize;
   165			void *base;
   166	
   167			if (!folio)
   168				break;
   169	
   170			fsize = folioq_folio_size(folioq, slot);
 > 171			if (skip >= fsize)
   172				goto next;
   173			base = kmap_local_folio(folio, skip);
   174			part = umin(len, PAGE_SIZE - skip % PAGE_SIZE);
   175			remain = step(base, progress, part, priv, priv2);
   176			kunmap_local(base);
   177			consumed = part - remain;
   178			len -= consumed;
   179			progress += consumed;
   180			skip += consumed;
   181			if (skip >= fsize) {
   182	next:
   183				skip = 0;
   184				slot++;
   185				if (slot == folioq_nr_slots(folioq) && folioq->next) {
   186					folioq = folioq->next;
   187					slot = 0;
   188				}
   189			}
   190			if (remain)
   191				break;
   192		} while (len);
   193	
   194		iter->folioq_slot = slot;
   195		iter->folioq = folioq;
   196		iter->iov_offset = skip;
   197		iter->count -= progress;
   198		return progress;
   199	}
   200	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Nathan Chancellor]

On Tue, Aug 12, 2025 at 02:55:55AM +0800, kernel test robot wrote:
> Hi Dominique,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on 8f5ae30d69d7543eee0d70083daf4de8fe15d585]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Dominique-Martinet-via-B4-Relay/iov_iter-iterate_folioq-fix-handling-of-offset-folio-size/20250811-154319
> base:   8f5ae30d69d7543eee0d70083daf4de8fe15d585
> patch link:    https://lore.kernel.org/r/20250811-iot_iter_folio-v1-1-d9c223adf93c%40codewreck.org
> patch subject: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size
> config: i386-buildonly-randconfig-002-20250811 (https://download.01.org/0day-ci/archive/20250812/202508120250.Eooq2ydr-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250812/202508120250.Eooq2ydr-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202508120250.Eooq2ydr-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from lib/iov_iter.c:14:
> >> include/linux/iov_iter.h:171:7: warning: variable 'remain' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
>      171 |                 if (skip >= fsize)
>          |                     ^~~~~~~~~~~~~
>    include/linux/iov_iter.h:190:7: note: uninitialized use occurs here
>      190 |                 if (remain)
>          |                     ^~~~~~
>    include/linux/iov_iter.h:171:3: note: remove the 'if' if its condition is always false
>      171 |                 if (skip >= fsize)
>          |                 ^~~~~~~~~~~~~~~~~~
>      172 |                         goto next;
>          |                         ~~~~~~~~~
>    include/linux/iov_iter.h:163:22: note: initialize the variable 'remain' to silence this warning
>      163 |                 size_t part, remain, consumed;
>          |                                    ^
>          |                                     = 0
>    1 warning generated.

I see this in -next now, should remain be zero initialized or is there
some other fix that is needed?

> vim +171 include/linux/iov_iter.h
> 
>    143	
>    144	/*
>    145	 * Handle ITER_FOLIOQ.
>    146	 */
>    147	static __always_inline
>    148	size_t iterate_folioq(struct iov_iter *iter, size_t len, void *priv, void *priv2,
>    149			      iov_step_f step)
>    150	{
>    151		const struct folio_queue *folioq = iter->folioq;
>    152		unsigned int slot = iter->folioq_slot;
>    153		size_t progress = 0, skip = iter->iov_offset;
>    154	
>    155		if (slot == folioq_nr_slots(folioq)) {
>    156			/* The iterator may have been extended. */
>    157			folioq = folioq->next;
>    158			slot = 0;
>    159		}
>    160	
>    161		do {
>    162			struct folio *folio = folioq_folio(folioq, slot);
>    163			size_t part, remain, consumed;
>    164			size_t fsize;
>    165			void *base;
>    166	
>    167			if (!folio)
>    168				break;
>    169	
>    170			fsize = folioq_folio_size(folioq, slot);
>  > 171			if (skip >= fsize)
>    172				goto next;
>    173			base = kmap_local_folio(folio, skip);
>    174			part = umin(len, PAGE_SIZE - skip % PAGE_SIZE);
>    175			remain = step(base, progress, part, priv, priv2);
>    176			kunmap_local(base);
>    177			consumed = part - remain;
>    178			len -= consumed;
>    179			progress += consumed;
>    180			skip += consumed;
>    181			if (skip >= fsize) {
>    182	next:
>    183				skip = 0;
>    184				slot++;
>    185				if (slot == folioq_nr_slots(folioq) && folioq->next) {
>    186					folioq = folioq->next;
>    187					slot = 0;
>    188				}
>    189			}
>    190			if (remain)
>    191				break;
>    192		} while (len);
>    193	
>    194		iter->folioq_slot = slot;
>    195		iter->folioq = folioq;
>    196		iter->iov_offset = skip;
>    197		iter->count -= progress;
>    198		return progress;
>    199	}
>    200	
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Dominique Martinet]

Nathan Chancellor wrote on Tue, Aug 12, 2025 at 10:16:33PM -0700:
> >    1 warning generated.
> 
> I see this in -next now, should remain be zero initialized or is there
> some other fix that is needed?

A zero-initialization is fine, I sent a v2 with zero-initialization
fixed yesterday:
https://lkml.kernel.org/r/20250812-iot_iter_folio-v2-1-f99423309478@codewreck.org

(and I'll send a v3 with the goto replaced with a bigger if later today
as per David's request)

I assume Andrew will pick it up eventually?
-- 
Dominique Martinet | Asmadeus

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Andy Shevchenko]

On Wed, Aug 13, 2025 at 02:34:25PM +0900, Dominique Martinet wrote:
> Nathan Chancellor wrote on Tue, Aug 12, 2025 at 10:16:33PM -0700:
> > >    1 warning generated.
> > 
> > I see this in -next now, should remain be zero initialized or is there
> > some other fix that is needed?
> 
> A zero-initialization is fine, I sent a v2 with zero-initialization
> fixed yesterday:
> https://lkml.kernel.org/r/20250812-iot_iter_folio-v2-1-f99423309478@codewreck.org
> 
> (and I'll send a v3 with the goto replaced with a bigger if later today
> as per David's request)
> 
> I assume Andrew will pick it up eventually?

I hope this to happen sooner as it broke my builds too (I always do now `make W=1`
and suggest all developers should follow).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Dominique Martinet]

Andy Shevchenko wrote on Wed, Aug 13, 2025 at 03:39:09PM +0200:
> > I assume Andrew will pick it up eventually?
> 
> I hope this to happen sooner as it broke my builds too (I always do now `make W=1`
> and suggest all developers should follow).

I actually test with W=1 too, but somehow this warning doesn't show up
in my build, I'm not quite sure why :/
(even if I try clang like the test robot... But there's plenty of
other warnings all around everywhere else, so I agree this is all way
too manual)

Anyway, sorry about it...
-- 
Dominique

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[David Howells]

Dominique Martinet <asmadeus@codewreck.org> wrote:

> I assume Andrew will pick it up eventually?

These might be more a Christian/VFS thing.

David

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Andy Shevchenko]

On Wed, Aug 13, 2025 at 10:45:33PM +0900, Dominique Martinet wrote:
> Andy Shevchenko wrote on Wed, Aug 13, 2025 at 03:39:09PM +0200:
> > > I assume Andrew will pick it up eventually?
> > 
> > I hope this to happen sooner as it broke my builds too (I always do now `make W=1`
> > and suggest all developers should follow).
> 
> I actually test with W=1 too, but somehow this warning doesn't show up
> in my build, I'm not quite sure why :/
> (even if I try clang like the test robot... But there's plenty of
> other warnings all around everywhere else, so I agree this is all way
> too manual)

Depends on your config, last few releases I was specifically targetting x86
defconfigs (32- and 64-bit) to be build with `make W=1`. There are a couple of
changes that are still pending, but otherwise it builds with GCC and clang.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Paul E. McKenney]

On Wed, Aug 13, 2025 at 03:39:09PM +0200, Andy Shevchenko wrote:
> On Wed, Aug 13, 2025 at 02:34:25PM +0900, Dominique Martinet wrote:
> > Nathan Chancellor wrote on Tue, Aug 12, 2025 at 10:16:33PM -0700:
> > > >    1 warning generated.
> > > 
> > > I see this in -next now, should remain be zero initialized or is there
> > > some other fix that is needed?
> > 
> > A zero-initialization is fine, I sent a v2 with zero-initialization
> > fixed yesterday:
> > https://lkml.kernel.org/r/20250812-iot_iter_folio-v2-1-f99423309478@codewreck.org
> > 
> > (and I'll send a v3 with the goto replaced with a bigger if later today
> > as per David's request)
> > 
> > I assume Andrew will pick it up eventually?
> 
> I hope this to happen sooner as it broke my builds too (I always do now `make W=1`
> and suggest all developers should follow).

This build failure is showing up in my testing as well.

In the service of preventing bisection issues, would it be possible to
fold the fix into the original patch?

							Thanx, Paul

Re: [PATCH 1/2] iov_iter: iterate_folioq: fix handling of offset >= folio size

[Dominique Martinet]

Andy Shevchenko wrote on Wed, Aug 13, 2025 at 04:52:39PM +0300:
> > I actually test with W=1 too, but somehow this warning doesn't show up
> > in my build, I'm not quite sure why :/
> > (even if I try clang like the test robot... But there's plenty of
> > other warnings all around everywhere else, so I agree this is all way
> > too manual)
> 
> Depends on your config, last few releases I was specifically targetting x86
> defconfigs (32- and 64-bit) to be build with `make W=1`. There are a couple of
> changes that are still pending, but otherwise it builds with GCC and clang.

I meant it the other way around: the warning isn't showing up on master
+ these patches for my config.

But now I double-checked, 'CC=clang make W=1' doesn't actually use
clang, I should have tried 'make CC=clang W=1'...
And, yeah, it just doesn't show up with gcc so I'll know it's better to
check both compilers...

Paul E. McKenney wrote on Wed, Aug 13, 2025 at 04:04:19PM -0700:
> > I hope this to happen sooner as it broke my builds too (I always do now `make W=1`
> > and suggest all developers should follow).
> 
> This build failure is showing up in my testing as well.
> 
> In the service of preventing bisection issues, would it be possible to
> fold the fix into the original patch?

Andrew just picked v3 up, so there won't be any such problem, and -next
will stop failing after today's update

-- 
Dominique Martinet | Asmadeus