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From b952c8f1da6f8597736c0e040565830139369359 Mon Sep 17 00:00:00 2001
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From: Stefano Garzarella <sgarzare@redhat.com>
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Date: Tue, 14 Feb 2023 18:16:21 +0100
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Subject: [PATCH] block: temporarily hold the new AioContext of bs_top in
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bdrv_append()
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RH-Author: Stefano Garzarella <sgarzare@redhat.com>
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RH-MergeRequest: 153: block: temporarily hold the new AioContext of bs_top in bdrv_append()
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RH-Bugzilla: 2168209
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RH-Acked-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Commit: [1/1] 5b190426d996e8c9f7a781bd97aee8d25756dbd3 (sgarzarella/qemu-kvm-c-9-s)
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bdrv_append() is called with bs_top AioContext held, but
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bdrv_attach_child_noperm() could change the AioContext of bs_top.
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bdrv_replace_node_noperm() calls bdrv_drained_begin() starting from
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commit 2398747128 ("block: Don't poll in bdrv_replace_child_noperm()").
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bdrv_drained_begin() can call BDRV_POLL_WHILE that assumes the new lock
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is taken, so let's temporarily hold the new AioContext to prevent QEMU
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from failing in BDRV_POLL_WHILE when it tries to release the wrong
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AioContext.
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Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2168209
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Reported-by: Aihua Liang <aliang@redhat.com>
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Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
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Message-Id: <20230214171621.11574-1-sgarzare@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 60d90bf43c169b9d1dbcb17ed794b7b02c6862b1)
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Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
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---
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block.c | 23 +++++++++++++++++++++++
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1 file changed, 23 insertions(+)
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diff --git a/block.c b/block.c
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index 0d78711416..9e1dcb9e47 100644
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--- a/block.c
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+++ b/block.c
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@@ -5275,6 +5275,8 @@ int bdrv_drop_filter(BlockDriverState *bs, Error **errp)
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* child.
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*
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* This function does not create any image files.
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+ *
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+ * The caller must hold the AioContext lock for @bs_top.
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*/
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int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
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Error **errp)
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@@ -5282,11 +5284,14 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
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int ret;
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BdrvChild *child;
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Transaction *tran = tran_new();
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+ AioContext *old_context, *new_context = NULL;
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GLOBAL_STATE_CODE();
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assert(!bs_new->backing);
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+ old_context = bdrv_get_aio_context(bs_top);
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+
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child = bdrv_attach_child_noperm(bs_new, bs_top, "backing",
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&child_of_bds, bdrv_backing_role(bs_new),
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tran, errp);
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@@ -5295,6 +5300,19 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
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goto out;
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}
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+ /*
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+ * bdrv_attach_child_noperm could change the AioContext of bs_top.
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+ * bdrv_replace_node_noperm calls bdrv_drained_begin, so let's temporarily
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+ * hold the new AioContext, since bdrv_drained_begin calls BDRV_POLL_WHILE
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+ * that assumes the new lock is taken.
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+ */
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+ new_context = bdrv_get_aio_context(bs_top);
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+
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+ if (old_context != new_context) {
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+ aio_context_release(old_context);
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+ aio_context_acquire(new_context);
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+ }
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+
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ret = bdrv_replace_node_noperm(bs_top, bs_new, true, tran, errp);
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if (ret < 0) {
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goto out;
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@@ -5306,6 +5324,11 @@ out:
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bdrv_refresh_limits(bs_top, NULL, NULL);
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+ if (new_context && old_context != new_context) {
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+ aio_context_release(new_context);
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+ aio_context_acquire(old_context);
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+ }
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+
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return ret;
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}
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--
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2.31.1
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