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aead9dc9d1
qemu/block
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Paolo Bonzini aead9dc9d1 graph-lock: Introduce a lock to protect block graph operations 
Block layer graph operations are always run under BQL in the main loop.
This is proved by the assertion qemu_in_main_thread() and its wrapper
macro GLOBAL_STATE_CODE.

However, there are also concurrent coroutines running in other iothreads
that always try to traverse the graph. Currently this is protected
(among various other things) by the AioContext lock, but once this is
removed, we need to make sure that reads do not happen while modifying
the graph.

We distinguish between writer (main loop, under BQL) that modifies the
graph, and readers (all other coroutines running in various AioContext),
that go through the graph edges, reading ->parents and->children.

The writer (main loop) has "exclusive" access, so it first waits for any
current read to finish, and then prevents incoming ones from entering
while it has the exclusive access.

The readers (coroutines in multiple AioContext) are free to access the
graph as long the writer is not modifying the graph. In case it is, they
go in a CoQueue and sleep until the writer is done.

If a coroutine changes AioContext, the counter in the original and new
AioContext are left intact, since the writer does not care where the
reader is, but only if there is one.

As a result, some AioContexts might have a negative reader count, to
balance the positive count of the AioContext that took the lock.  This
also means that when an AioContext is deleted it may have a nonzero
reader count. In that case we transfer the count to a global shared
counter so that the writer is always aware of all readers.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20221207131838.239125-3-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2022-12-15 16:07:43 +01:00
..
export qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
monitor qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
accounting.c block: add missed block_acct_setup with new block device init procedure 2022-09-30 18:42:34 +02:00
aio_task.c block/aio_task: assert max_busy_tasks is greater than 0 2021-10-05 18:56:41 +02:00
amend.c block/amend: Keep strong reference to BDS 2022-03-04 18:18:26 +01:00
backup.c backup: remove incorrect coroutine_fn annotation 2022-10-27 20:14:11 +02:00
blkdebug.c qemu-config: Make config_parse_qdict() return bool 2022-12-14 16:19:35 +01:00
blkio.c block/blkio: Set BlockDriver::has_variable_length to false 2022-11-10 14:52:36 +01:00
blklogwrites.c block/blklogwrites: don't care to remove bs->file child on failure 2022-10-27 20:14:11 +02:00
blkreplay.c block: introduce bdrv_open_file_child() helper 2022-10-27 20:14:11 +02:00
blkverify.c Block layer patches 2022-10-30 15:15:12 -04:00
block-backend.c block-backend: replace bdrv_*_above with blk_*_above 2022-12-15 16:07:43 +01:00
block-copy.c block-copy: add coroutine_fn annotations 2022-12-15 16:07:43 +01:00
block-gen.h block-coroutine-wrapper.py: support also basic return types 2022-12-15 16:07:43 +01:00
block-ram-registrar.c block: add BlockRAMRegistrar 2022-10-26 14:56:42 -04:00
bochs.c block: introduce bdrv_open_file_child() helper 2022-10-27 20:14:11 +02:00
cloop.c block: introduce bdrv_open_file_child() helper 2022-10-27 20:14:11 +02:00
commit.c block-backend: replace bdrv_*_above with blk_*_above 2022-12-15 16:07:43 +01:00
copy-before-write.c Miscellaneous patches for 2022-12-14 2022-12-15 10:13:46 +00:00
copy-before-write.h block/copy-before-write.h: global state API + assertions 2022-03-04 18:18:25 +01:00
copy-on-read.c block: introduce bdrv_open_file_child() helper 2022-10-27 20:14:11 +02:00
copy-on-read.h Clean up ill-advised or unusual header guards 2022-05-11 16:50:01 +02:00
coroutines.h block: rename generated_co_wrapper in co_wrapper_mixed 2022-12-15 16:07:43 +01:00
create.c block_int-common.h: assertions in the callers of BlockDriver function pointers 2022-03-04 18:18:25 +01:00
crypto.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
crypto.h nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
curl.c curl: add missing coroutine_fn annotations 2022-10-07 12:11:41 +02:00
dirty-bitmap.c block/dirty-bitmap: convert coroutine-only functions to co_wrapper 2022-12-15 16:07:43 +01:00
dmg-bz2.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
dmg-lzfse.c block: Remove unused include 2020-11-09 15:44:21 +01:00
dmg.c dmg: warn when opening dmg images containing blocks of unknown type 2022-11-06 09:48:50 +01:00
dmg.h Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
file-posix.c block: add BDRV_REQ_REGISTERED_BUF request flag 2022-10-26 14:56:42 -04:00
file-win32.c block: use int64_t instead of uint64_t in driver write handlers 2021-09-29 13:46:31 -05:00
filter-compress.c block: introduce bdrv_open_file_child() helper 2022-10-27 20:14:11 +02:00
gluster.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
graph-lock.c graph-lock: Introduce a lock to protect block graph operations 2022-12-15 16:07:43 +01:00
io_uring.c block/io_uring: revert "Use io_uring_register_ring_fd() to skip fd operations" 2022-10-27 20:14:11 +02:00
io.c block: Factor out bdrv_drain_all_begin_nopoll() 2022-12-15 16:07:43 +01:00
iscsi-opts.c modules: add block module annotations 2021-07-09 18:20:27 +02:00
iscsi.c iscsi: add missing coroutine_fn annotations 2022-10-07 12:11:40 +02:00
linux-aio.c misc: fix commonly doubled up words 2022-08-01 11:58:02 +02:00
meson.build graph-lock: Introduce a lock to protect block graph operations 2022-12-15 16:07:43 +01:00
mirror.c block/mirror: Fix NULL s->job in active writes 2022-11-10 13:33:55 +01:00
nbd.c block: add BDRV_REQ_REGISTERED_BUF request flag 2022-10-26 14:56:42 -04:00
nfs.c block/nfs: Fix 32-bit Windows build 2022-10-27 20:14:11 +02:00
null.c block: use int64_t instead of uint64_t in driver write handlers 2021-09-29 13:46:31 -05:00
nvme.c block: return errors from bdrv_register_buf() 2022-10-26 14:56:42 -04:00
parallels-ext.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
parallels.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
parallels.h parallels: support bitmap extension for read-only mode 2021-03-08 14:56:55 +01:00
preallocate.c block: introduce bdrv_open_file_child() helper 2022-10-27 20:14:11 +02:00
progress_meter.c progressmeter: protect with a mutex 2021-06-25 14:24:24 +03:00
qapi-sysemu.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
qapi.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
qcow2-bitmap.c qcow2: manually add more coroutine_fn annotations 2022-10-27 20:14:11 +02:00
qcow2-cache.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
qcow2-cluster.c qcow2: switch to *_co_* functions 2022-10-27 20:14:11 +02:00
qcow2-refcount.c qcow2: switch to *_co_* functions 2022-10-27 20:14:11 +02:00
qcow2-snapshot.c qcow2: switch to *_co_* functions 2022-10-27 20:14:11 +02:00
qcow2-threads.c qcow2: add zstd cluster compression 2020-05-13 14:20:31 +02:00
qcow2.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
qcow2.h qcow2: manually add more coroutine_fn annotations 2022-10-27 20:14:11 +02:00
qcow.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
qed-check.c block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
qed-cluster.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed-l2-cache.c osdep: Move memalign-related functions to their own header 2022-03-07 13:16:49 +00:00
qed-table.c qed: switch to *_co_* functions 2022-10-27 20:14:11 +02:00
qed.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
qed.h qed: Simplify backing reads 2020-07-06 10:34:14 +02:00
quorum.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
raw-format.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
rbd.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
replication.c block: Drain individual nodes during reopen 2022-12-15 16:07:42 +01:00
reqlist.c block/reqlist: add reqlist_wait_all() 2022-03-07 09:33:30 +01:00
snapshot-access.c block: Manipulate bs->file / bs->backing pointers in .attach/.detach 2022-10-27 20:14:11 +02:00
snapshot.c block/snapshot: drop indirection around bdrv_snapshot_fallback_ptr 2022-10-27 20:14:11 +02:00
ssh.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
stream.c stream: Replace subtree drain with a single node drain 2022-12-15 16:07:42 +01:00
throttle-groups.c block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytes 2021-02-03 08:14:00 -06:00
throttle.c block: Revert .bdrv_drained_begin/end to non-coroutine_fn 2022-12-15 16:07:42 +01:00
trace-events nbd: trace long NBD operations 2022-06-29 10:57:02 +03:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
vdi.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
vhdx-endian.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
vhdx-log.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
vhdx.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
vhdx.h block/vhdx: Use IEC binary prefixes for size constants 2019-04-30 15:29:00 +02:00
vmdk.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
vpc.c block: bdrv_create_file is a coroutine_fn 2022-12-15 16:07:43 +01:00
vvfat.c block/vvfat: Unify the mkdir() call 2022-10-31 20:37:58 +00:00
win32-aio.c osdep: Move memalign-related functions to their own header 2022-03-07 13:16:49 +00:00
write-threshold.c write-threshold: deal with includes 2021-05-14 16:14:10 +02:00