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65 lines
2.5 KiB
65 lines
2.5 KiB
1 month ago
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From 6c8da957fd534b3546354a8b8252c01cf9ee3511 Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Mon, 6 May 2024 15:06:22 -0400
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Subject: [PATCH 14/14] aio: warn about iohandler_ctx special casing
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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RH-MergeRequest: 253: Revert "monitor: use aio_co_reschedule_self()"
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RH-Jira: RHEL-43409 RHEL-43410
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: Hanna Czenczek <hreitz@redhat.com>
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RH-Commit: [2/2] 895231553731f09f51275c1abbf50c3440fe977f (kmwolf/centos-qemu-kvm)
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The main loop has two AioContexts: qemu_aio_context and iohandler_ctx.
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The main loop runs them both, but nested aio_poll() calls on
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qemu_aio_context exclude iohandler_ctx.
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Which one should qemu_get_current_aio_context() return when called from
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the main loop? Document that it's always qemu_aio_context.
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This has subtle effects on functions that use
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qemu_get_current_aio_context(). For example, aio_co_reschedule_self()
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does not work when moving from iohandler_ctx to qemu_aio_context because
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qemu_get_current_aio_context() does not differentiate these two
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AioContexts.
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Document this in order to reduce the chance of future bugs.
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-ID: <20240506190622.56095-3-stefanha@redhat.com>
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Reviewed-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit e669e800fc9ef8806af5c5578249ab758a4f8a5a)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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---
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include/block/aio.h | 6 ++++++
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1 file changed, 6 insertions(+)
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diff --git a/include/block/aio.h b/include/block/aio.h
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index 8378553eb9..4ee81936ed 100644
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--- a/include/block/aio.h
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+++ b/include/block/aio.h
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@@ -629,6 +629,9 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co);
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*
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* Move the currently running coroutine to new_ctx. If the coroutine is already
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* running in new_ctx, do nothing.
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+ *
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+ * Note that this function cannot reschedule from iohandler_ctx to
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+ * qemu_aio_context.
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*/
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void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
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@@ -661,6 +664,9 @@ void aio_co_enter(AioContext *ctx, Coroutine *co);
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* If called from an IOThread this will be the IOThread's AioContext. If
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* called from the main thread or with the "big QEMU lock" taken it
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* will be the main loop AioContext.
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+ *
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+ * Note that the return value is never the main loop's iohandler_ctx and the
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+ * return value is the main loop AioContext instead.
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*/
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AioContext *qemu_get_current_aio_context(void);
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--
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2.39.3
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