| Message ID | 20190702231302.60727-1-nhuck@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: mm: Fix dead assignment of old_pte | expand |
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: clang-built-linux@googlegroups.com > Signed-off-by: Nathan Huckleberry <nhuck@google.com> > --- > 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
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 <natechancellor@gmail.com> 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: clang-built-linux@googlegroups.com > > Signed-off-by: Nathan Huckleberry <nhuck@google.com> > > --- > > 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 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20190702232459.GA14941%40archlinux-epyc.
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); }
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: clang-built-linux@googlegroups.com Signed-off-by: Nathan Huckleberry <nhuck@google.com> --- arch/arm64/include/asm/pgtable.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)