f1eed34ac7
This version includes both the AioContext lock and the block graph lock, so there might be some deadlocks lurking. It's not possible to disable the block graph lock like was done in QEMU 8.1, because there are no changes like the function bdrv_schedule_unref() that require it. QEMU 9.0 will finally get rid of the AioContext locking. During live-restore with a VirtIO SCSI drive with iothread there is a known racy deadlock related to the AioContext lock. Not new [1], but not sure if more likely now. Should be fixed in QEMU 9.0. The block graph lock comes with annotations that can be checked by clang's TSA. This required changes to the block drivers, i.e. alloc-track, pbs, zeroinit as well as taking the appropriate locks in pve-backup, savevm-async, vma-reader. Local variable shadowing is prohibited via a compiler flag now, required slight adaptation in vma.c. Major changes only affect alloc-track: * It is not possible to call a generated co-wrapper like bdrv_get_info() while holding the block graph lock exclusively [0], which does happen during initialization of alloc-track when the backing hd is set and the refresh_limits driver callback is invoked. The bdrv_get_info() call to get the cluster size is moved to directly after opening the file child in track_open(). The important thing is that at least the request alignment for the write target is used, because then the RMW cycle in bdrv_pwritev will gather enough data from the backing file. Partial cluster allocations in the target are not a fundamental issue, because the driver returns its allocation status based on the bitmap, so any other data that maps to the same cluster will still be copied later by a stream job (or during writes to that cluster). * Replacing the node cannot be done in the track_co_change_backing_file() callback, because it is a coroutine and cannot hold the block graph lock exclusively. So it is moved to the stream job itself with the auto-remove option not having an effect anymore (qemu-server would always set it anyways). In the future, there could either be a special option for the stream job, or maybe the upcoming blockdev-replace QMP command can be used. Replacing the backing child is actually already done in the stream job, so no need to do it in the track_co_change_backing_file() callback. It also cannot be called from a coroutine. Looking at the implementation in the qcow2 driver, it doesn't seem to be intended to change the backing child itself, just update driver-internal state. Other changes: * alloc-track: Error out early when used without auto-remove. Since replacing the node now happens in the stream job, where the option cannot be read from (it's internal to the driver), it will always be treated as 'on'. Makes sure to have users beside qemu-server notice the change (should they even exist). The option can be fully dropped in the future while adding a version guard in qemu-server. * alloc-track: Avoid seemingly superfluous child permission update. Doesn't seem necessary nowadays (maybe after commit "alloc-track: fix deadlock during drop" where the dropping is not rescheduled and delayed anymore or some upstream change). Replacing the block node will already update the permissions of the new node (which was the file child before). Should there really be some issue, instead of having a drop state, this could also be just based off the fact whether there is still a backing child. Dumping the cumulative (shared) permissions for the BDS with a debug print yields the same values after this patch and with QEMU 8.1, namely 3 and 5. * PBS block driver: compile unconditionally. Proxmox VE always needs it and something in the build process changed to make it not enabled by default. Probably would need to move the build option to meson otherwise. * backup: job unreferencing during cleanup needs to happen outside of coroutine, so it was moved to before invoking the clean * mirror: Cherry-pick stable fix to avoid potential deadlock. * savevm-async: migrate_init now can fail, so propagate potential error. * savevm-async: compression counters are not accessible outside migration/ram-compress now, so drop code that prophylactically set it to zero. [0]: https://lore.kernel.org/qemu-devel/220be383-3b0d-4938-b584-69ad214e5d5d@proxmox.com/ [1]: https://lore.kernel.org/qemu-devel/e13b488e-bf13-44f2-acca-e724d14f43fd@proxmox.com/ Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
60 lines
2.4 KiB
Diff
60 lines
2.4 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Fabian Ebner <f.ebner@proxmox.com>
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Date: Wed, 2 Mar 2022 08:35:05 +0100
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Subject: [PATCH] block/backup: move bcs bitmap initialization to job creation
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For backing up the state of multiple disks from the same time, a job
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for each disk has to be created. It's convenient if the jobs don't
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have to be started at the same time and if operation of the VM can be
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resumed after job creation. This would lead to a window between job
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creation and running the job, where writes can happen. But no writes
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should happen between setting up the copy-before-write filter and
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setting up the block copy state bitmap, because then new writes would
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just pass through.
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Commit 06e0a9c16405c0a4c1eca33cf286cc04c42066a2 moved initalization of
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the bitmap to setting up the copy-before-write filter when sync_mode
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is not MIRROR_SYNC_MODE_BITMAP. Ensure that the bitmap is initialized
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upon job creation for the remaining case too, by moving the
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backup_init_bcs_bitmap call to backup_job_create.
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Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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---
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block/backup.c | 8 ++++----
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1 file changed, 4 insertions(+), 4 deletions(-)
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diff --git a/block/backup.c b/block/backup.c
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index 8aae5836d7..2516eac5a7 100644
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--- a/block/backup.c
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+++ b/block/backup.c
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@@ -237,8 +237,8 @@ static void backup_init_bcs_bitmap(BackupBlockJob *job)
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true);
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} else if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
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/*
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- * We can't hog the coroutine to initialize this thoroughly.
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- * Set a flag and resume work when we are able to yield safely.
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+ * Initialization is costly here. Simply set a flag and let the
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+ * backup_run coroutine resume work once it can yield safely.
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*/
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block_copy_set_skip_unallocated(job->bcs, true);
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}
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@@ -252,8 +252,6 @@ static int coroutine_fn backup_run(Job *job, Error **errp)
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BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
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int ret;
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- backup_init_bcs_bitmap(s);
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-
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if (s->sync_mode == MIRROR_SYNC_MODE_TOP) {
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int64_t offset = 0;
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int64_t count;
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@@ -501,6 +499,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
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&error_abort);
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bdrv_graph_wrunlock(target);
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+ backup_init_bcs_bitmap(job);
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+
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return &job->common;
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error:
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