From: Vladimir Murzin <vladimir.murzin@arm.com>
To: Nathan Huckleberry <nhuck@google.com>,
catalin.marinas@arm.com, will@kernel.org
Cc: clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] arm64: mm: Fix dead assignment of old_pte
Date: Wed, 3 Jul 2019 09:31:04 +0100 [thread overview]
Message-ID: <1895c6b5-645d-6a63-d486-efa20d6879db@arm.com> (raw)
In-Reply-To: <20190702234135.78780-1-nhuck@google.com>
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: clang-built-linux@googlegroups.com
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> ---
> 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);
> }
>
next prev parent reply other threads:[~2019-07-03 8:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-02 23:13 [PATCH] " Nathan Huckleberry
2019-07-02 23:24 ` Nathan Chancellor
2019-07-02 23:26 ` Nathan Huckleberry
2019-07-02 23:41 ` [PATCH v2] " Nathan Huckleberry
2019-07-03 8:31 ` Vladimir Murzin [this message]
2019-07-03 9:17 ` Will Deacon
2019-07-03 11:23 ` Mark Rutland
2019-07-03 17:24 ` Nathan Huckleberry
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