When a timer is fired a pending I/O request is restarted and
tg->any_timer_armed is reset so other requests can be scheduled.
However we're resetting any_timer_armed first in timer_cb() before
the request is actually restarted, and there's a window between both
moments in which another thread can arm the same timer, hitting an
assertion in throttle_group_restart_queue().
This can be solved by deferring the reset of tg->any_timer_armed to
the moment when the queue is actually restarted, which is protected by
tg->lock, preventing other threads from arming the timer before that.
In addition to that, throttle_group_restart_tgm() is also updated to
hold tg->lock while the timer is being inspected. Here we consider
three different scenarios:
- If the tgm has a timer set, fire it immediately
- If another tgm has a timer set, restart the queue anyway
- If there is no timer set in this group then simulate a timer that
fires immediately, by setting tg->any_timer_armed in order to
prevent other threads from arming a timer in the meantime.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3194
Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <825598ef34ad384d936da19d634eda75598508f7.1773316842.git.berto@igalia.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
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