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block: remove AioContext locking

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This is the big patch that removes
aio_context_acquire()/aio_context_release() from the block layer and
affected block layer users.

There isn't a clean way to split this patch and the reviewers are likely
the same group of people, so I decided to do it in one patch.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Message-ID: <20231205182011.1976568-7-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-12-05 13:20:03 -05:00 • committed by Kevin Wolf
parent 6bc30f1949
commit b49f4755c7
41 changed files with 104 additions and 1169 deletions
Download patch file Download diff file Expand all files Collapse all files

34
migration/block.c
View file

@ -66,7 +66,7 @@ typedef struct BlkMigDevState {
/* Protected by block migration lock. */
int64_t completed_sectors;
/* During migration this is protected by iothread lock / AioContext.
/* During migration this is protected by bdrv_dirty_bitmap_lock().
* Allocation and free happen during setup and cleanup respectively.
*/
BdrvDirtyBitmap *dirty_bitmap;
@ -101,7 +101,7 @@ typedef struct BlkMigState {
int prev_progress;
int bulk_completed;
/* Lock must be taken _inside_ the iothread lock and any AioContexts. */
/* Lock must be taken _inside_ the iothread lock. */
QemuMutex lock;
} BlkMigState;
@ -270,7 +270,6 @@ static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
if (bmds->shared_base) {
qemu_mutex_lock_iothread();
aio_context_acquire(blk_get_aio_context(bb));
/* Skip unallocated sectors; intentionally treats failure or
* partial sector as an allocated sector */
while (cur_sector < total_sectors &&
@ -281,7 +280,6 @@ static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
}
cur_sector += count >> BDRV_SECTOR_BITS;
}
aio_context_release(blk_get_aio_context(bb));
qemu_mutex_unlock_iothread();
}
@ -313,21 +311,16 @@ static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
block_mig_state.submitted++;
blk_mig_unlock();
/* We do not know if bs is under the main thread (and thus does
* not acquire the AioContext when doing AIO) or rather under
* dataplane. Thus acquire both the iothread mutex and the
* AioContext.
*
* This is ugly and will disappear when we make bdrv_* thread-safe,
* without the need to acquire the AioContext.
/*
* The migration thread does not have an AioContext. Lock the BQL so that
* I/O runs in the main loop AioContext (see
* qemu_get_current_aio_context()).
*/
qemu_mutex_lock_iothread();
aio_context_acquire(blk_get_aio_context(bmds->blk));
bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, cur_sector * BDRV_SECTOR_SIZE,
nr_sectors * BDRV_SECTOR_SIZE);
blk->aiocb = blk_aio_preadv(bb, cur_sector * BDRV_SECTOR_SIZE, &blk->qiov,
0, blk_mig_read_cb, blk);
aio_context_release(blk_get_aio_context(bmds->blk));
qemu_mutex_unlock_iothread();
bmds->cur_sector = cur_sector + nr_sectors;
@ -512,7 +505,7 @@ static void blk_mig_reset_dirty_cursor(void)
}
}
/* Called with iothread lock and AioContext taken. */
/* Called with iothread lock taken. */
static int mig_save_device_dirty(QEMUFile *f, BlkMigDevState *bmds,
int is_async)
@ -606,9 +599,7 @@ static int blk_mig_save_dirty_block(QEMUFile *f, int is_async)
int ret = 1;
QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
aio_context_acquire(blk_get_aio_context(bmds->blk));
ret = mig_save_device_dirty(f, bmds, is_async);
aio_context_release(blk_get_aio_context(bmds->blk));
if (ret <= 0) {
break;
}
@ -666,9 +657,9 @@ static int64_t get_remaining_dirty(void)
int64_t dirty = 0;
QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
aio_context_acquire(blk_get_aio_context(bmds->blk));
bdrv_dirty_bitmap_lock(bmds->dirty_bitmap);
dirty += bdrv_get_dirty_count(bmds->dirty_bitmap);
aio_context_release(blk_get_aio_context(bmds->blk));
bdrv_dirty_bitmap_unlock(bmds->dirty_bitmap);
}
return dirty;
@ -681,7 +672,6 @@ static void block_migration_cleanup_bmds(void)
{
BlkMigDevState *bmds;
BlockDriverState *bs;
AioContext *ctx;
unset_dirty_tracking();
@ -693,13 +683,7 @@ static void block_migration_cleanup_bmds(void)
bdrv_op_unblock_all(bs, bmds->blocker);
}
error_free(bmds->blocker);
/* Save ctx, because bmds->blk can disappear during blk_unref. */
ctx = blk_get_aio_context(bmds->blk);
aio_context_acquire(ctx);
blk_unref(bmds->blk);
aio_context_release(ctx);
g_free(bmds->blk_name);
g_free(bmds->aio_bitmap);
g_free(bmds);

3
migration/migration-hmp-cmds.c
View file

@ -852,14 +852,11 @@ static void vm_completion(ReadLineState *rs, const char *str)
for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
SnapshotInfoList *snapshots, *snapshot;
AioContext *ctx = bdrv_get_aio_context(bs);
bool ok = false;
aio_context_acquire(ctx);
if (bdrv_can_snapshot(bs)) {
ok = bdrv_query_snapshot_info_list(bs, &snapshots, NULL) == 0;
}
aio_context_release(ctx);
if (!ok) {
continue;
}

22
migration/savevm.c
View file

@ -3049,7 +3049,6 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
int saved_vm_running;
uint64_t vm_state_size;
g_autoptr(GDateTime) now = g_date_time_new_now_local();
AioContext *aio_context;
GLOBAL_STATE_CODE();
@ -3092,7 +3091,6 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
if (bs == NULL) {
return false;
}
aio_context = bdrv_get_aio_context(bs);
saved_vm_running = runstate_is_running();
@ -3101,8 +3099,6 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
bdrv_drain_all_begin();
aio_context_acquire(aio_context);
memset(sn, 0, sizeof(*sn));
/* fill auxiliary fields */
@ -3139,14 +3135,6 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
goto the_end;
}
/* The bdrv_all_create_snapshot() call that follows acquires the AioContext
* for itself. BDRV_POLL_WHILE() does not support nested locking because
* it only releases the lock once. Therefore synchronous I/O will deadlock
* unless we release the AioContext before bdrv_all_create_snapshot().
*/
aio_context_release(aio_context);
aio_context = NULL;
ret = bdrv_all_create_snapshot(sn, bs, vm_state_size,
has_devices, devices, errp);
if (ret < 0) {
@ -3157,10 +3145,6 @@ bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
ret = 0;
the_end:
if (aio_context) {
aio_context_release(aio_context);
}
bdrv_drain_all_end();
if (saved_vm_running) {
@ -3258,7 +3242,6 @@ bool load_snapshot(const char *name, const char *vmstate,
QEMUSnapshotInfo sn;
QEMUFile *f;
int ret;
AioContext *aio_context;
MigrationIncomingState *mis = migration_incoming_get_current();
if (!bdrv_all_can_snapshot(has_devices, devices, errp)) {
@ -3278,12 +3261,9 @@ bool load_snapshot(const char *name, const char *vmstate,
if (!bs_vm_state) {
return false;
}
aio_context = bdrv_get_aio_context(bs_vm_state);
/* Don't even try to load empty VM states */
aio_context_acquire(aio_context);
ret = bdrv_snapshot_find(bs_vm_state, &sn, name);
aio_context_release(aio_context);
if (ret < 0) {
return false;
} else if (sn.vm_state_size == 0) {
@ -3320,10 +3300,8 @@ bool load_snapshot(const char *name, const char *vmstate,
ret = -EINVAL;
goto err_drain;
}
aio_context_acquire(aio_context);
ret = qemu_loadvm_state(f);
migration_incoming_state_destroy();
aio_context_release(aio_context);
bdrv_drain_all_end();