Re: [PATCH 1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: patchwork-bot+linux-riscv@kernel.org
Cc: Suren Baghdasaryan <surenb@google.com>,
	linux-riscv@lists.infradead.org, akpm@linux-foundation.org,
	willy@infradead.org, will@kernel.org, catalin.marinas@arm.com,
	palmer@dabbelt.com, mpe@ellerman.id.au,
	christophe.leroy@csgroup.eu, agordeev@linux.ibm.com,
	gerald.schaefer@linux.ibm.com, dave.hansen@linux.intel.com,
	luto@kernel.org, peterz@infradead.org, x86@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
Date: Sat, 20 Jan 2024 21:15:01 +0000	[thread overview]
Message-ID: <Zaw31DVa9q3JZASo@shell.armlinux.org.uk> (raw)
In-Reply-To: <170578498755.24348.16166096320323933297.git-patchwork-notify@kernel.org>

On Sat, Jan 20, 2024 at 09:09:47PM +0000, patchwork-bot+linux-riscv@kernel.org wrote:
> Hello:
> 
> This patch was applied to riscv/linux.git (fixes)
> by Andrew Morton <akpm@linux-foundation.org>:
> 
> On Tue, 26 Dec 2023 13:46:10 -0800 you wrote:
> > A test [1] in Android test suite started failing after [2] was merged.
> > It turns out that after handling a major fault under per-VMA lock, the
> > process major fault counter does not register that fault as major.
> > Before [2] read faults would be done under mmap_lock, in which case
> > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes
> > mm_account_fault() to account the fault as major once retry completes.
> > With per-VMA locks we often retry because a fault can't be handled
> > without locking the whole mm using mmap_lock. Therefore such retries
> > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2]
> > because we can now handle read major faults under per-VMA lock and
> > upon retry the fact there was a major fault gets lost. Fix this by
> > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if
> > VM_FAULT_MAJOR was returned. Ideally we would use an additional
> > VM_FAULT bit to indicate the reason for the retry (could not handle
> > under per-VMA lock vs other reason) but this simpler solution seems
> > to work, so keeping it simple.
> > 
> > [...]
> 
> Here is the summary with links:
>   - [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
>     https://git.kernel.org/riscv/c/46e714c729c8
> 
> You are awesome, thank you!

Now that 32-bit ARM has support for the per-VMA lock, does that also
need to be patched?

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