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9pfs: fix concurrent v9fs_reclaim_fd() calls

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Even though this function is serialized to be always called from main
thread, v9fs_reclaim_fd() is dispatching the coroutine to a worker thread
in between via its v9fs_co_*() calls, hence leading to the situation where
v9fs_reclaim_fd() is effectively executed multiple times simultaniously,
which renders its LRU algorithm useless and causes high latency.

Fix this by adding a simple boolean variable to ensure this function is
only called once at a time. No synchronization needed for this boolean
variable as this function is only entered and returned on main thread.

Fixes: 7a46274529 ('hw/9pfs: Add file descriptor reclaim support')
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <5c622067efd66dd4ee5eca740dcf263f41db20b2.1741339452.git.qemu_oss@crudebyte.com>
This commit is contained in:
Christian Schoenebeck 2025-03-07 10:22:56 +01:00
parent 5134cf9b5d
commit 61da38db70
2 changed files with 11 additions and 0 deletions
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10
hw/9pfs/9p.c
View file

@ -435,6 +435,12 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
GHashTableIter iter;
gpointer fid;
/* prevent multiple coroutines running this function simultaniously */
if (s->reclaiming) {
return;
}
s->reclaiming = true;
g_hash_table_iter_init(&iter, s->fids);
QSLIST_HEAD(, V9fsFidState) reclaim_list =
@ -510,6 +516,8 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
*/
put_fid(pdu, f);
}
s->reclaiming = false;
}
/*
@ -4324,6 +4332,8 @@ int v9fs_device_realize_common(V9fsState *s, const V9fsTransport *t,
s->ctx.fst = &fse->fst;
fsdev_throttle_init(s->ctx.fst);
s->reclaiming = false;
rc = 0;
out:
if (rc) {

1
hw/9pfs/9p.h
View file

@ -362,6 +362,7 @@ struct V9fsState {
uint64_t qp_ndevices; /* Amount of entries in qpd_table. */
uint16_t qp_affix_next;
uint64_t qp_fullpath_next;
bool reclaiming;
};
/* 9p2000.L open flags */