mirror of
https://github.com/qemu/qemu.git
synced 2025-10-31 04:06:46 +00:00
fc8796465c
When ->poll() succeeds the AioHandler is placed on the ready list with
revents set to the magic value 0. This magic value causes
aio_dispatch_handler() to invoke ->poll_ready() instead of ->io_read()
for G_IO_IN or ->io_write() for G_IO_OUT.
This magic value 0 hack works for the IOThread where AioHandlers are
placed on ->ready_list and processed by aio_dispatch_ready_handlers().
It does not work for the main loop where all AioHandlers are processed
by aio_dispatch_handlers(), even those that are not ready and have a
revents value of 0.
As a result the main loop invokes ->poll_ready() on AioHandlers that are
not ready. These spurious ->poll_ready() calls waste CPU cycles and
could lead to crashes if the code assumes ->poll() must have succeeded
before ->poll_ready() is called (a reasonable asumption but I haven't
seen it in practice).
Stop using revents to track whether ->poll_ready() will be called on an
AioHandler. Introduce a separate AioHandler->poll_ready field instead.
This eliminates spurious ->poll_ready() calls in the main loop.
Fixes: 826cc32423 ("aio-posix: split poll check from ready handler")
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reported-by: Jason Wang <jasowang@redhat.com>
Tested-by: Jason Wang <jasowang@redhat.com>
Message-id: 20220223155703.136833-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
84 lines
2.1 KiB
C
84 lines
2.1 KiB
C
/*
|
|
* AioContext POSIX event loop implementation internal APIs
|
|
*
|
|
* Copyright IBM, Corp. 2008
|
|
* Copyright Red Hat, Inc. 2020
|
|
*
|
|
* Authors:
|
|
* Anthony Liguori <aliguori@us.ibm.com>
|
|
*
|
|
* This work is licensed under the terms of the GNU GPL, version 2. See
|
|
* the COPYING file in the top-level directory.
|
|
*
|
|
* Contributions after 2012-01-13 are licensed under the terms of the
|
|
* GNU GPL, version 2 or (at your option) any later version.
|
|
*/
|
|
|
|
#ifndef AIO_POSIX_H
|
|
#define AIO_POSIX_H
|
|
|
|
#include "block/aio.h"
|
|
|
|
struct AioHandler {
|
|
GPollFD pfd;
|
|
IOHandler *io_read;
|
|
IOHandler *io_write;
|
|
AioPollFn *io_poll;
|
|
IOHandler *io_poll_ready;
|
|
IOHandler *io_poll_begin;
|
|
IOHandler *io_poll_end;
|
|
void *opaque;
|
|
QLIST_ENTRY(AioHandler) node;
|
|
QLIST_ENTRY(AioHandler) node_ready; /* only used during aio_poll() */
|
|
QLIST_ENTRY(AioHandler) node_deleted;
|
|
QLIST_ENTRY(AioHandler) node_poll;
|
|
#ifdef CONFIG_LINUX_IO_URING
|
|
QSLIST_ENTRY(AioHandler) node_submitted;
|
|
unsigned flags; /* see fdmon-io_uring.c */
|
|
#endif
|
|
int64_t poll_idle_timeout; /* when to stop userspace polling */
|
|
bool poll_ready; /* has polling detected an event? */
|
|
bool is_external;
|
|
};
|
|
|
|
/* Add a handler to a ready list */
|
|
void aio_add_ready_handler(AioHandlerList *ready_list, AioHandler *node,
|
|
int revents);
|
|
|
|
extern const FDMonOps fdmon_poll_ops;
|
|
|
|
#ifdef CONFIG_EPOLL_CREATE1
|
|
bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd);
|
|
void fdmon_epoll_setup(AioContext *ctx);
|
|
void fdmon_epoll_disable(AioContext *ctx);
|
|
#else
|
|
static inline bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static inline void fdmon_epoll_setup(AioContext *ctx)
|
|
{
|
|
}
|
|
|
|
static inline void fdmon_epoll_disable(AioContext *ctx)
|
|
{
|
|
}
|
|
#endif /* !CONFIG_EPOLL_CREATE1 */
|
|
|
|
#ifdef CONFIG_LINUX_IO_URING
|
|
bool fdmon_io_uring_setup(AioContext *ctx);
|
|
void fdmon_io_uring_destroy(AioContext *ctx);
|
|
#else
|
|
static inline bool fdmon_io_uring_setup(AioContext *ctx)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static inline void fdmon_io_uring_destroy(AioContext *ctx)
|
|
{
|
|
}
|
|
#endif /* !CONFIG_LINUX_IO_URING */
|
|
|
|
#endif /* AIO_POSIX_H */
|