Oops I forgot moving the variable declaration would cause a warning.
Will send a V2.
Thanks,
Nathan Huckleberry
On Tue, Jul 2, 2019 at 4:25 PM Nathan Chancellor
<[email protected]> wrote:
>
> On Tue, Jul 02, 2019 at 04:13:02PM -0700, 'Nathan Huckleberry' via Clang Built Linux wrote:
> > When analyzed with the clang static analyzer the
> > following warning occurs
> >
> > line 251, column 2
> > Value stored to 'old_pte' is never read
> >
> > This warning is repeated every time pgtable.h is
> > included by another file and produces ~3500
> > extra warnings.
> >
> > Moving old_pte into preprocessor guard.
> >
> > Cc: [email protected]
> > Signed-off-by: Nathan Huckleberry <[email protected]>
> > ---
> > arch/arm64/include/asm/pgtable.h | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > index fca26759081a..42ca4fc67f27 100644
> > --- a/arch/arm64/include/asm/pgtable.h
> > +++ b/arch/arm64/include/asm/pgtable.h
> > @@ -238,8 +238,6 @@ extern void __sync_icache_dcache(pte_t pteval);
> > static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > pte_t *ptep, pte_t pte)
> > {
> > - pte_t old_pte;
> > -
> > if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
> > __sync_icache_dcache(pte);
> >
> > @@ -248,8 +246,11 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > * hardware updates of the pte (ptep_set_access_flags safely changes
> > * valid ptes without going through an invalid entry).
> > */
> > + #if IS_ENABLED(CONFIG_DEBUG_VM)
> > + pte_t old_pte;
> > +
> > old_pte = READ_ONCE(*ptep);
> > - if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(old_pte) && pte_valid(pte) &&
> > + if (pte_valid(old_pte) && pte_valid(pte) &&
> > (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) {
> > VM_WARN_ONCE(!pte_young(pte),
> > "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> > @@ -258,6 +259,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> > __func__, pte_val(old_pte), pte_val(pte));
> > }
> > + #endif
> >
> > set_pte(ptep, pte);
> > }
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
> >
>
> Hi Nathan,
>
> This does not apply on -next because of https://git.kernel.org/arm64/c/9b604722059039a1a3ff69fb8dfd024264046024.
> I would get into the habit of testing -next to see if the warning is
> present there first because someone may have independently fixed it
> already (I'd be surprised if it wasn't fixed by that commit from a quick
> glance).
>
> Additionally, when I do apply this patch to mainline and build, I see
> the following warning:
>
> In file included from /home/nathan/cbl/linux/arch/arm64/kernel/asm-offsets.c:10:
> In file included from /home/nathan/cbl/linux/include/linux/arm_sdei.h:14:
> In file included from /home/nathan/cbl/linux/include/acpi/ghes.h:5:
> In file included from /home/nathan/cbl/linux/include/acpi/apei.h:9:
> In file included from /home/nathan/cbl/linux/include/linux/acpi.h:34:
> In file included from /home/nathan/cbl/linux/include/acpi/acpi_io.h:5:
> In file included from /home/nathan/cbl/linux/include/linux/io.h:13:
> In file included from /home/nathan/cbl/linux/arch/arm64/include/asm/io.h:18:
> /home/nathan/cbl/linux/arch/arm64/include/asm/pgtable.h:250:8: warning: ISO C90 forbids mixing declarations and code [-Wdeclaration-after-statement]
> pte_t old_pte;
> ^
> 1 warning generated.
>
> Cheers,
> Nathan
>
> --
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When analyzed with the clang static analyzer the
following warning occurs
line 251, column 2
Value stored to 'old_pte' is never read
This warning is repeated every time pgtable.h is
included by another file and produces ~3500
extra warnings.
Moving old_pte into preprocessor guard.
Cc: [email protected]
Signed-off-by: Nathan Huckleberry <[email protected]>
---
Changes from v1 -> v2
* Added scope to avoid [-Wdeclaration-after-statement]
arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++++-----------
1 file changed, 16 insertions(+), 11 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index fca26759081a..12b7f08db40d 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -238,8 +238,6 @@ extern void __sync_icache_dcache(pte_t pteval);
static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
- pte_t old_pte;
-
if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
__sync_icache_dcache(pte);
@@ -248,16 +246,23 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
* hardware updates of the pte (ptep_set_access_flags safely changes
* valid ptes without going through an invalid entry).
*/
- old_pte = READ_ONCE(*ptep);
- if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(old_pte) && pte_valid(pte) &&
- (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) {
- VM_WARN_ONCE(!pte_young(pte),
- "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
- __func__, pte_val(old_pte), pte_val(pte));
- VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
- "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
- __func__, pte_val(old_pte), pte_val(pte));
+ #if IS_ENABLED(CONFIG_DEBUG_VM)
+ {
+ pte_t old_pte;
+
+ old_pte = READ_ONCE(*ptep);
+ if (pte_valid(old_pte) && pte_valid(pte) &&
+ (mm == current->active_mm ||
+ atomic_read(&mm->mm_users) > 1)) {
+ VM_WARN_ONCE(!pte_young(pte),
+ "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
+ __func__, pte_val(old_pte), pte_val(pte));
+ VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
+ "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
+ __func__, pte_val(old_pte), pte_val(pte));
+ }
}
+ #endif
set_pte(ptep, pte);
}
--
2.22.0.410.gd8fdbe21b5-goog
On 7/3/19 12:41 AM, Nathan Huckleberry wrote:
> When analyzed with the clang static analyzer the
> following warning occurs
>
> line 251, column 2
> Value stored to 'old_pte' is never read
>
> This warning is repeated every time pgtable.h is
> included by another file and produces ~3500
> extra warnings.
>
> Moving old_pte into preprocessor guard.
I'm wondering if it is a case for __maybe_unused?
Something like:
- pte_t old_pte;
+ pte_t __maybe_unused old_pte;
Cheers
Vladimir
>
> Cc: [email protected]
> Signed-off-by: Nathan Huckleberry <[email protected]>
> ---
> Changes from v1 -> v2
> * Added scope to avoid [-Wdeclaration-after-statement]
> arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++++-----------
> 1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index fca26759081a..12b7f08db40d 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -238,8 +238,6 @@ extern void __sync_icache_dcache(pte_t pteval);
> static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, pte_t pte)
> {
> - pte_t old_pte;
> -
> if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
> __sync_icache_dcache(pte);
>
> @@ -248,16 +246,23 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> * hardware updates of the pte (ptep_set_access_flags safely changes
> * valid ptes without going through an invalid entry).
> */
> - old_pte = READ_ONCE(*ptep);
> - if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(old_pte) && pte_valid(pte) &&
> - (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) {
> - VM_WARN_ONCE(!pte_young(pte),
> - "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> - VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> - "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> + #if IS_ENABLED(CONFIG_DEBUG_VM)
> + {
> + pte_t old_pte;
> +
> + old_pte = READ_ONCE(*ptep);
> + if (pte_valid(old_pte) && pte_valid(pte) &&
> + (mm == current->active_mm ||
> + atomic_read(&mm->mm_users) > 1)) {
> + VM_WARN_ONCE(!pte_young(pte),
> + "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> + VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> + "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> + }
> }
> + #endif
>
> set_pte(ptep, pte);
> }
>
On Tue, Jul 02, 2019 at 04:41:35PM -0700, Nathan Huckleberry wrote:
> When analyzed with the clang static analyzer the
> following warning occurs
>
> line 251, column 2
> Value stored to 'old_pte' is never read
>
> This warning is repeated every time pgtable.h is
> included by another file and produces ~3500
> extra warnings.
Does this warning actually trigger with linux-next?
Will
On Tue, Jul 02, 2019 at 04:41:35PM -0700, Nathan Huckleberry wrote:
> When analyzed with the clang static analyzer the
> following warning occurs
>
> line 251, column 2
> Value stored to 'old_pte' is never read
>
> This warning is repeated every time pgtable.h is
> included by another file and produces ~3500
> extra warnings.
>
> Moving old_pte into preprocessor guard.
>
> Cc: [email protected]
> Signed-off-by: Nathan Huckleberry <[email protected]>
> ---
> Changes from v1 -> v2
> * Added scope to avoid [-Wdeclaration-after-statement]
> arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++++-----------
> 1 file changed, 16 insertions(+), 11 deletions(-)
As Will asked, does this also trigger in linux-next?
I rewrote this code to avoid to only perform the READ_ONCE() when we'd
use the value, and IIUC that may be sufficient to avoid the warning:
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=9b604722059039a1a3ff69fb8dfd024264046024
Thanks,
Mark.
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index fca26759081a..12b7f08db40d 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -238,8 +238,6 @@ extern void __sync_icache_dcache(pte_t pteval);
> static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, pte_t pte)
> {
> - pte_t old_pte;
> -
> if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
> __sync_icache_dcache(pte);
>
> @@ -248,16 +246,23 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> * hardware updates of the pte (ptep_set_access_flags safely changes
> * valid ptes without going through an invalid entry).
> */
> - old_pte = READ_ONCE(*ptep);
> - if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(old_pte) && pte_valid(pte) &&
> - (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) {
> - VM_WARN_ONCE(!pte_young(pte),
> - "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> - VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> - "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> + #if IS_ENABLED(CONFIG_DEBUG_VM)
> + {
> + pte_t old_pte;
> +
> + old_pte = READ_ONCE(*ptep);
> + if (pte_valid(old_pte) && pte_valid(pte) &&
> + (mm == current->active_mm ||
> + atomic_read(&mm->mm_users) > 1)) {
> + VM_WARN_ONCE(!pte_young(pte),
> + "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> + VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> + "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> + }
> }
> + #endif
>
> set_pte(ptep, pte);
> }
> --
> 2.22.0.410.gd8fdbe21b5-goog
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Warning is not triggered in next. Looks like this patch is unnecessary.
Thanks,
Nathan Huckleberry
On Wed, Jul 3, 2019 at 4:23 AM Mark Rutland <[email protected]> wrote:
>
> On Tue, Jul 02, 2019 at 04:41:35PM -0700, Nathan Huckleberry wrote:
> > When analyzed with the clang static analyzer the
> > following warning occurs
> >
> > line 251, column 2
> > Value stored to 'old_pte' is never read
> >
> > This warning is repeated every time pgtable.h is
> > included by another file and produces ~3500
> > extra warnings.
> >
> > Moving old_pte into preprocessor guard.
> >
> > Cc: [email protected]
> > Signed-off-by: Nathan Huckleberry <[email protected]>
> > ---
> > Changes from v1 -> v2
> > * Added scope to avoid [-Wdeclaration-after-statement]
> > arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++++-----------
> > 1 file changed, 16 insertions(+), 11 deletions(-)
>
> As Will asked, does this also trigger in linux-next?
>
> I rewrote this code to avoid to only perform the READ_ONCE() when we'd
> use the value, and IIUC that may be sufficient to avoid the warning:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=9b604722059039a1a3ff69fb8dfd024264046024
>
> Thanks,
> Mark.
>
> >
> > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > index fca26759081a..12b7f08db40d 100644
> > --- a/arch/arm64/include/asm/pgtable.h
> > +++ b/arch/arm64/include/asm/pgtable.h
> > @@ -238,8 +238,6 @@ extern void __sync_icache_dcache(pte_t pteval);
> > static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > pte_t *ptep, pte_t pte)
> > {
> > - pte_t old_pte;
> > -
> > if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
> > __sync_icache_dcache(pte);
> >
> > @@ -248,16 +246,23 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > * hardware updates of the pte (ptep_set_access_flags safely changes
> > * valid ptes without going through an invalid entry).
> > */
> > - old_pte = READ_ONCE(*ptep);
> > - if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(old_pte) && pte_valid(pte) &&
> > - (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) {
> > - VM_WARN_ONCE(!pte_young(pte),
> > - "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> > - __func__, pte_val(old_pte), pte_val(pte));
> > - VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> > - "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> > - __func__, pte_val(old_pte), pte_val(pte));
> > + #if IS_ENABLED(CONFIG_DEBUG_VM)
> > + {
> > + pte_t old_pte;
> > +
> > + old_pte = READ_ONCE(*ptep);
> > + if (pte_valid(old_pte) && pte_valid(pte) &&
> > + (mm == current->active_mm ||
> > + atomic_read(&mm->mm_users) > 1)) {
> > + VM_WARN_ONCE(!pte_young(pte),
> > + "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> > + __func__, pte_val(old_pte), pte_val(pte));
> > + VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> > + "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> > + __func__, pte_val(old_pte), pte_val(pte));
> > + }
> > }
> > + #endif
> >
> > set_pte(ptep, pte);
> > }
> > --
> > 2.22.0.410.gd8fdbe21b5-goog
> >
> >
> > _______________________________________________
> > linux-arm-kernel mailing list
> > [email protected]
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel