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105 lines
3.8 KiB
105 lines
3.8 KiB
From afa842e9fdf6e1d6e5d5785679a22779632142bd Mon Sep 17 00:00:00 2001
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From: Hanna Czenczek <hreitz@redhat.com>
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Date: Fri, 2 Feb 2024 15:47:54 +0100
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Subject: [PATCH 03/22] block-backend: Allow concurrent context changes
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RH-Author: Hanna Czenczek <hreitz@redhat.com>
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RH-MergeRequest: 222: Allow concurrent BlockBackend context changes
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RH-Jira: RHEL-24593
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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: [1/2] 9e1b535f60f7afa94a0817dc3e71136e41631c71 (hreitz/qemu-kvm-c-9-s)
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Since AioContext locks have been removed, a BlockBackend's AioContext
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may really change at any time (only exception is that it is often
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confined to a drained section, as noted in this patch). Therefore,
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blk_get_aio_context() cannot rely on its root node's context always
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matching that of the BlockBackend.
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In practice, whether they match does not matter anymore anyway: Requests
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can be sent to BDSs from any context, so anyone who requests the BB's
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context should have no reason to require the root node to have the same
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context. Therefore, we can and should remove the assertion to that
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effect.
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In addition, because the context can be set and queried from different
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threads concurrently, it has to be accessed with atomic operations.
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Buglink: https://issues.redhat.com/browse/RHEL-19381
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Suggested-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
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Message-ID: <20240202144755.671354-2-hreitz@redhat.com>
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Reviewed-by: Stefan Hajnoczi <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 ad893672027ffe26db498947d70cde6d4f58a111)
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---
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block/block-backend.c | 22 +++++++++++-----------
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1 file changed, 11 insertions(+), 11 deletions(-)
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diff --git a/block/block-backend.c b/block/block-backend.c
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index 209eb07528..9c4de79e6b 100644
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--- a/block/block-backend.c
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+++ b/block/block-backend.c
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@@ -44,7 +44,7 @@ struct BlockBackend {
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char *name;
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int refcnt;
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BdrvChild *root;
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- AioContext *ctx;
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+ AioContext *ctx; /* access with atomic operations only */
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DriveInfo *legacy_dinfo; /* null unless created by drive_new() */
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QTAILQ_ENTRY(BlockBackend) link; /* for block_backends */
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QTAILQ_ENTRY(BlockBackend) monitor_link; /* for monitor_block_backends */
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@@ -2414,22 +2414,22 @@ void blk_op_unblock_all(BlockBackend *blk, Error *reason)
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}
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}
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+/**
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+ * Return BB's current AioContext. Note that this context may change
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+ * concurrently at any time, with one exception: If the BB has a root node
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+ * attached, its context will only change through bdrv_try_change_aio_context(),
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+ * which creates a drained section. Therefore, incrementing such a BB's
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+ * in-flight counter will prevent its context from changing.
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+ */
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AioContext *blk_get_aio_context(BlockBackend *blk)
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{
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- BlockDriverState *bs;
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IO_CODE();
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if (!blk) {
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return qemu_get_aio_context();
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}
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- bs = blk_bs(blk);
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- if (bs) {
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- AioContext *ctx = bdrv_get_aio_context(blk_bs(blk));
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- assert(ctx == blk->ctx);
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- }
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-
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- return blk->ctx;
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+ return qatomic_read(&blk->ctx);
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}
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int blk_set_aio_context(BlockBackend *blk, AioContext *new_context,
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@@ -2442,7 +2442,7 @@ int blk_set_aio_context(BlockBackend *blk, AioContext *new_context,
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GLOBAL_STATE_CODE();
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if (!bs) {
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- blk->ctx = new_context;
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+ qatomic_set(&blk->ctx, new_context);
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return 0;
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}
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@@ -2471,7 +2471,7 @@ static void blk_root_set_aio_ctx_commit(void *opaque)
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AioContext *new_context = s->new_ctx;
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ThrottleGroupMember *tgm = &blk->public.throttle_group_member;
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- blk->ctx = new_context;
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+ qatomic_set(&blk->ctx, new_context);
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if (tgm->throttle_state) {
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throttle_group_detach_aio_context(tgm);
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throttle_group_attach_aio_context(tgm, new_context);
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--
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2.39.3
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