On Sat, Jan 20, 2024 at 1:15 PM Russell King (Oracle)
[off-list ref] wrote:

On Sat, Jan 20, 2024 at 09:09:47PM +0000, patchwork-bot+linux-riscv@kernel.org wrote:

quoted

Hello:

This patch was applied to riscv/linux.git (fixes)
by Andrew Morton [off-list ref]:

On Tue, 26 Dec 2023 13:46:10 -0800 you wrote:

quoted

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?

Yes, I think so. I missed the ARM32 change that added support for
per-VMA locks. Will post a similar patch for it tomorrow.
Thanks,
Suren.

--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!