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From 59f0fc4b8011298bc542eb23cca385d83d1963cd Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Wed, 10 Oct 2018 20:22:02 +0100
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Subject: [PATCH 36/49] block: Add missing locking in bdrv_co_drain_bh_cb()
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20181010202213.7372-24-kwolf@redhat.com>
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Patchwork-id: 82613
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O-Subject: [RHEL-8 qemu-kvm PATCH 33/44] block: Add missing locking in bdrv_co_drain_bh_cb()
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Bugzilla: 1637976
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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bdrv_do_drained_begin/end() assume that they are called with the
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AioContext lock of bs held. If we call drain functions from a coroutine
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with the AioContext lock held, we yield and schedule a BH to move out of
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coroutine context. This means that the lock for the home context of the
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coroutine is released and must be re-acquired in the bottom half.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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(cherry picked from commit aa1361d54aac43094b98024b8b6c804eb6e41661)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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block/io.c | 15 +++++++++++++++
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include/qemu/coroutine.h | 5 +++++
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util/qemu-coroutine.c | 5 +++++
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3 files changed, 25 insertions(+)
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diff --git a/block/io.c b/block/io.c
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index d404088..19db35e 100644
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--- a/block/io.c
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+++ b/block/io.c
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@@ -286,6 +286,18 @@ static void bdrv_co_drain_bh_cb(void *opaque)
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BlockDriverState *bs = data->bs;
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if (bs) {
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+ AioContext *ctx = bdrv_get_aio_context(bs);
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+ AioContext *co_ctx = qemu_coroutine_get_aio_context(co);
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+
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+ /*
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+ * When the coroutine yielded, the lock for its home context was
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+ * released, so we need to re-acquire it here. If it explicitly
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+ * acquired a different context, the lock is still held and we don't
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+ * want to lock it a second time (or AIO_WAIT_WHILE() would hang).
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+ */
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+ if (ctx == co_ctx) {
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+ aio_context_acquire(ctx);
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+ }
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bdrv_dec_in_flight(bs);
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if (data->begin) {
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bdrv_do_drained_begin(bs, data->recursive, data->parent,
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@@ -294,6 +306,9 @@ static void bdrv_co_drain_bh_cb(void *opaque)
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bdrv_do_drained_end(bs, data->recursive, data->parent,
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data->ignore_bds_parents);
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}
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+ if (ctx == co_ctx) {
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+ aio_context_release(ctx);
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+ }
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} else {
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assert(data->begin);
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bdrv_drain_all_begin();
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diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
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index 6f8a487..9801e7f 100644
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--- a/include/qemu/coroutine.h
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+++ b/include/qemu/coroutine.h
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@@ -90,6 +90,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co);
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void coroutine_fn qemu_coroutine_yield(void);
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/**
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+ * Get the AioContext of the given coroutine
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+ */
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+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);
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+
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+/**
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* Get the currently executing coroutine
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*/
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Coroutine *coroutine_fn qemu_coroutine_self(void);
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diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c
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index 1ba4191..2295928 100644
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--- a/util/qemu-coroutine.c
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+++ b/util/qemu-coroutine.c
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@@ -198,3 +198,8 @@ bool qemu_coroutine_entered(Coroutine *co)
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{
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return co->caller;
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}
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+
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+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co)
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+{
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+ return co->ctx;
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+}
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--
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1.8.3.1
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