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xen-bus/block: explicitly assign event channels to an AioContext

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It is not safe to close an event channel from the QEMU main thread when
that channel's poller is running in IOThread context.

This patch adds a new xen_device_set_event_channel_context() function
to explicitly assign the channel AioContext, and modifies
xen_device_bind_event_channel() to initially assign the channel's poller
to the QEMU main thread context. The code in xen-block's dataplane is
then modified to assign the channel to IOThread context during
xen_block_dataplane_start() and de-assign it during in
xen_block_dataplane_stop(), such that the channel is always assigned
back to main thread context before it is closed. aio_set_fd_handler()
already deals with all the necessary synchronization when moving an fd
between AioContext-s so no extra code is needed to manage this.

Reported-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20191216143451.19024-1-pdurrant@amazon.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This commit is contained in:
Paul Durrant 2019-12-16 14:34:51 +00:00 • committed by Anthony PERARD
parent b8030af450
commit 32d0b7be68
3 changed files with 45 additions and 7 deletions
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5
include/hw/xen/xen-bus.h
View file

@ -128,10 +128,13 @@ void xen_device_copy_grant_refs(XenDevice *xendev, bool to_domain,
typedef bool (*XenEventHandler)(void *opaque);
XenEventChannel *xen_device_bind_event_channel(XenDevice *xendev,
AioContext *ctx,
unsigned int port,
XenEventHandler handler,
void *opaque, Error **errp);
void xen_device_set_event_channel_context(XenDevice *xendev,
XenEventChannel *channel,
AioContext *ctx,
Error **errp);
void xen_device_notify_event_channel(XenDevice *xendev,
XenEventChannel *channel,
Error **errp);