motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-30 13:31:52 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

coroutine: avoid co_queue_wakeup recursion

Browse source 
qemu_aio_coroutine_enter() is (indirectly) called recursively when
processing co_queue_wakeup.  This can lead to stack exhaustion.

This patch rewrites co_queue_wakeup in an iterative fashion (instead of
recursive) with bounded memory usage to prevent stack exhaustion.

qemu_co_queue_run_restart() is inlined into qemu_aio_coroutine_enter()
and the qemu_coroutine_enter() call is turned into a loop to avoid
recursion.

There is one change that is worth mentioning:  Previously, when
coroutine A queued coroutine B, qemu_co_queue_run_restart() entered
coroutine B from coroutine A.  If A was terminating then it would still
stay alive until B yielded.  After this patch B is entered by A's parent
so that a A can be deleted immediately if it is terminating.

It is safe to make this change since B could never interact with A if it
was terminating anyway.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20180322152834.12656-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2018-03-22 15:28:33 +00:00
parent 67a74148d8
commit c40a254570
4 changed files with 50 additions and 78 deletions
Download patch file Download diff file Expand all files Collapse all files

34
util/qemu-coroutine-lock.c
View file

@ -68,40 +68,6 @@ void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock)
}
}
/**
* qemu_co_queue_run_restart:
*
* Enter each coroutine that was previously marked for restart by
* qemu_co_queue_next() or qemu_co_queue_restart_all(). This function is
* invoked by the core coroutine code when the current coroutine yields or
* terminates.
*/
void qemu_co_queue_run_restart(Coroutine *co)
{
Coroutine *next;
QSIMPLEQ_HEAD(, Coroutine) tmp_queue_wakeup =
QSIMPLEQ_HEAD_INITIALIZER(tmp_queue_wakeup);
trace_qemu_co_queue_run_restart(co);
/* Because "co" has yielded, any coroutine that we wakeup can resume it.
* If this happens and "co" terminates, co->co_queue_wakeup becomes
* invalid memory. Therefore, use a temporary queue and do not touch
* the "co" coroutine as soon as you enter another one.
*
* In its turn resumed "co" can populate "co_queue_wakeup" queue with
* new coroutines to be woken up. The caller, who has resumed "co",
* will be responsible for traversing the same queue, which may cause
* a different wakeup order but not any missing wakeups.
*/
QSIMPLEQ_CONCAT(&tmp_queue_wakeup, &co->co_queue_wakeup);
while ((next = QSIMPLEQ_FIRST(&tmp_queue_wakeup))) {
QSIMPLEQ_REMOVE_HEAD(&tmp_queue_wakeup, co_queue_next);
qemu_coroutine_enter(next);
}
}
static bool qemu_co_queue_do_restart(CoQueue *queue, bool single)
{
Coroutine *next;