| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <Z5PfOZ1D6dNKTzw6@x1n>
Date: Fri, 24 Jan 2025 13:43:05 -0500
From: Peter Xu <peterx@...hat.com>
To: kernel test robot <lkp@...el.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Memory Management List <linux-mm@...ck.org>,
Will Deacon <will@...nel.org>
Subject: Re: mm/gup.c:778:15: sparse: sparse: cast to non-scalar
On Fri, Jan 24, 2025 at 10:01:40AM +0800, kernel test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: e0b1f59142746f74476a03040f745329c8355a7e
> commit: e6fd5564c07c3c749ff3d1b2aa35540b4047e395 mm/gup: cache p4d in follow_p4d_mask()
> date: 9 months ago
> config: alpha-randconfig-r112-20250124 (https://download.01.org/0day-ci/archive/20250124/202501240922.a4YzQD7u-lkp@intel.com/config)
> compiler: alpha-linux-gcc (GCC) 14.2.0
> reproduce: (https://download.01.org/0day-ci/archive/20250124/202501240922.a4YzQD7u-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@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202501240922.a4YzQD7u-lkp@intel.com/
>
> sparse warnings: (new ones prefixed by >>)
> >> mm/gup.c:778:15: sparse: sparse: cast to non-scalar
> >> mm/gup.c:778:15: sparse: sparse: cast from non-scalar
> mm/gup.c: note: in included file (through include/linux/mm.h):
> include/linux/pgtable.h:315:16: sparse: sparse: cast to non-scalar
> include/linux/pgtable.h:315:16: sparse: sparse: cast from non-scalar
> include/linux/pgtable.h:315:16: sparse: sparse: cast to non-scalar
> include/linux/pgtable.h:315:16: sparse: sparse: cast from non-scalar
> mm/gup.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/mm.h):
> include/linux/page-flags.h:241:46: sparse: sparse: self-comparison always evaluates to false
> mm/gup.c:682:9: sparse: sparse: context imbalance in 'follow_page_pte' - unexpected unlock
> mm/gup.c: note: in included file (through include/linux/mm.h):
> include/linux/pgtable.h:322:16: sparse: sparse: cast to non-scalar
> include/linux/pgtable.h:322:16: sparse: sparse: cast from non-scalar
> include/linux/pgtable.h:315:16: sparse: sparse: cast to non-scalar
> include/linux/pgtable.h:315:16: sparse: sparse: cast from non-scalar
> mm/gup.c:911:18: sparse: sparse: context imbalance in 'get_gate_page' - unexpected unlock
>
> vim +778 mm/gup.c
>
> 769
> 770 static struct page *follow_p4d_mask(struct vm_area_struct *vma,
> 771 unsigned long address, pgd_t *pgdp,
> 772 unsigned int flags,
> 773 struct follow_page_context *ctx)
> 774 {
> 775 p4d_t *p4dp, p4d;
> 776
> 777 p4dp = p4d_offset(pgdp, address);
> > 778 p4d = READ_ONCE(*p4dp);
> 779 if (p4d_none(p4d))
> 780 return no_page_table(vma, flags);
> 781 BUILD_BUG_ON(p4d_huge(p4d));
> 782 if (unlikely(p4d_bad(p4d)))
> 783 return no_page_table(vma, flags);
> 784
> 785 return follow_pud_mask(vma, address, p4dp, flags, ctx);
> 786 }
> 787
There's one more similar sparse warning here, both reported today:
https://lore.kernel.org/all/202501241212.q9AAshQc-lkp@intel.com/
Firstly, I reproduced this sparse warning locally. And yes it yells about
that line, and even one more similar case of READ_ONCE().
The question is I thought READ_ONCE() should be ok to be used on things
like p4d_t, even if they can be structs / non-scalar types. At least from
sparse POV I cannot trigger similar sparse on non-alpha. So looks like
Alpha has something special.
Then I noticed that Alpha indeed has a custom definition of __READ_ONCE()
which is probably needed due to the mb():
#define __READ_ONCE(x) \
({ \
__unqual_scalar_typeof(x) __x = \
(*(volatile typeof(__x) *)(&(x))); \
mb(); \
(typeof(x))__x; \
})
I didn't obviously see yet on how that could affect sparse, if READ_ONCE()
works for non-scalar somehow on most of the rest archs.
I tried to switch to the default __READ_ONCE for alpha build (it misses
mb() so it isn't correct, but trying to figure out whether it'll trigger
similar sparse warning), then the warning is gone.
Then I found that this change can also work for alpha:
diff --git a/arch/alpha/include/asm/rwonce.h b/arch/alpha/include/asm/rwonce.h
index 35542bcf92b3..0d61183ff764 100644
--- a/arch/alpha/include/asm/rwonce.h
+++ b/arch/alpha/include/asm/rwonce.h
@@ -25,7 +25,7 @@
__unqual_scalar_typeof(x) __x = \
(*(volatile typeof(__x) *)(&(x))); \
mb(); \
- (typeof(x))__x; \
+ __x; \
})
I had a feeling that sparse somehow thinks the "typeof(x)" isn't the same
struct v.s. "__unqual_scalar_typeof(x)" above, even if IIUC the macro was
only trying to tear down type qualifiers. Especially in Alpha's case IIUC
p4d_t is a struct (in my case, STRICT_MM_TYPECHECKS=n):
typedef struct { pgd_t pgd; } p4d_t;
typedef unsigned long pgd_t;
So I suppose __unqual_scalar_typeof() should do nothing on a non-scalar
type.
So even if above oneliner seems to fix this specific sparse warning, I
don't really know how it worked.
I copied Will (who introduced both the alpha's __READ_ONCE, and the unqual
macro for generic code) in case he has some thoughts..
Thanks,
--
Peter Xu
Powered by blists - more mailing lists