On Fri, Apr 26, 2024 at 09:09:41PM +0100, Al Viro wrote:
> > + call_rcu(&drelease->rcu, delayed_mount_release);
>
> ... which is a bad idea, since call_rcu() callbacks are run
> from interrupt context. Which makes blocking in them a problem.
>
Thanks for the quick review.
Documentation/RCU/checklist.rst suggests switching to queue_rcu_work()
function in scenarios where the callback function can block. This seems
like it would fix the issue you found, while still providing similar
performance improvements.
workqueue:
perf stat -r 10 --null --pre 'mount -t tmpfs tmpfs mnt' -- umount -l mnt
0.003066 +- 0.000307 seconds time elapsed ( +- 10.02% )
callrcu:
perf stat -r 10 --null --pre 'mount -t tmpfs tmpfs mnt' -- umount -l mnt
0.0030812 +- 0.0000524 seconds time elapsed ( +- 1.70% )
Regards,
Lucas
