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block: Take graph rdlock in parts of reopen 

Reopen isn't easy with respect to locking because many of its functions
need to iterate the graph, some change it, and then you get some drains
in the middle where you can't hold any locks.

Therefore just documents most of the functions to be unlocked, and take
locks internally before accessing the graph.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-9-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2023-09-29 16:51:43 +02:00
parent a32e781838
commit ce433d2942
2 changed files with 43 additions and 27 deletions
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57
block.c
View File

@ -4314,8 +4314,8 @@ static int bdrv_reset_options_allowed(BlockDriverState *bs,
/*
* Returns true if @child can be reached recursively from @bs
*/
static bool bdrv_recurse_has_child(BlockDriverState *bs,
BlockDriverState *child)
static bool GRAPH_RDLOCK
bdrv_recurse_has_child(BlockDriverState *bs, BlockDriverState *child)
{
BdrvChild *c;
@ -4356,15 +4356,12 @@ static bool bdrv_recurse_has_child(BlockDriverState *bs,
*
* To be called with bs->aio_context locked.
*/
static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
BlockDriverState *bs,
QDict *options,
const BdrvChildClass *klass,
BdrvChildRole role,
bool parent_is_format,
QDict *parent_options,
int parent_flags,
bool keep_old_opts)
static BlockReopenQueue * GRAPH_RDLOCK
bdrv_reopen_queue_child(BlockReopenQueue *bs_queue, BlockDriverState *bs,
QDict *options, const BdrvChildClass *klass,
BdrvChildRole role, bool parent_is_format,
QDict *parent_options, int parent_flags,
bool keep_old_opts)
{
assert(bs != NULL);
@ -4376,6 +4373,11 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
GLOBAL_STATE_CODE();
/*
* Strictly speaking, draining is illegal under GRAPH_RDLOCK. We know that
* we've been called with bdrv_graph_rdlock_main_loop(), though, so it's ok
* in practice.
*/
bdrv_drained_begin(bs);
if (bs_queue == NULL) {
@ -4517,6 +4519,7 @@ BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
QDict *options, bool keep_old_opts)
{
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
return bdrv_reopen_queue_child(bs_queue, bs, options, NULL, 0, false,
NULL, 0, keep_old_opts);
@ -4736,9 +4739,10 @@ int bdrv_reopen_set_read_only(BlockDriverState *bs, bool read_only,
* Callers must make sure that their AioContext locking is still correct after
* this.
*/
static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
bool is_backing, Transaction *tran,
Error **errp)
static int GRAPH_UNLOCKED
bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
bool is_backing, Transaction *tran,
Error **errp)
{
BlockDriverState *bs = reopen_state->bs;
BlockDriverState *new_child_bs;
@ -4748,6 +4752,7 @@ static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
QObject *value;
const char *str;
AioContext *ctx, *old_ctx;
bool has_child;
int ret;
GLOBAL_STATE_CODE();
@ -4767,7 +4772,13 @@ static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
new_child_bs = bdrv_lookup_bs(NULL, str, errp);
if (new_child_bs == NULL) {
return -EINVAL;
} else if (bdrv_recurse_has_child(new_child_bs, bs)) {
}
bdrv_graph_rdlock_main_loop();
has_child = bdrv_recurse_has_child(new_child_bs, bs);
bdrv_graph_rdunlock_main_loop();
if (has_child) {
error_setg(errp, "Making '%s' a %s child of '%s' would create a "
"cycle", str, child_name, bs->node_name);
return -EINVAL;
@ -4866,9 +4877,9 @@ static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
* After calling this function, the transaction @change_child_tran may only be
* completed while holding a writer lock for the graph.
*/
static int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
BlockReopenQueue *queue,
Transaction *change_child_tran, Error **errp)
static int GRAPH_UNLOCKED
bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
Transaction *change_child_tran, Error **errp)
{
int ret = -1;
int old_flags;
@ -5010,6 +5021,8 @@ static int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
if (qdict_size(reopen_state->options)) {
const QDictEntry *entry = qdict_first(reopen_state->options);
GRAPH_RDLOCK_GUARD_MAINLOOP();
do {
QObject *new = entry->value;
QObject *old = qdict_get(reopen_state->bs->options, entry->key);
@ -5083,7 +5096,7 @@ error:
* makes them final by swapping the staging BlockDriverState contents into
* the active BlockDriverState contents.
*/
static void bdrv_reopen_commit(BDRVReopenState *reopen_state)
static void GRAPH_UNLOCKED bdrv_reopen_commit(BDRVReopenState *reopen_state)
{
BlockDriver *drv;
BlockDriverState *bs;
@ -5100,6 +5113,8 @@ static void bdrv_reopen_commit(BDRVReopenState *reopen_state)
drv->bdrv_reopen_commit(reopen_state);
}
GRAPH_RDLOCK_GUARD_MAINLOOP();
/* set BDS specific flags now */
qobject_unref(bs->explicit_options);
qobject_unref(bs->options);
@ -5121,9 +5136,7 @@ static void bdrv_reopen_commit(BDRVReopenState *reopen_state)
qdict_del(bs->explicit_options, "backing");
qdict_del(bs->options, "backing");
bdrv_graph_rdlock_main_loop();
bdrv_refresh_limits(bs, NULL, NULL);
bdrv_graph_rdunlock_main_loop();
bdrv_refresh_total_sectors(bs, bs->total_sectors);
}
@ -5131,7 +5144,7 @@ static void bdrv_reopen_commit(BDRVReopenState *reopen_state)
* Abort the reopen, and delete and free the staged changes in
* reopen_state
*/
static void bdrv_reopen_abort(BDRVReopenState *reopen_state)
static void GRAPH_UNLOCKED bdrv_reopen_abort(BDRVReopenState *reopen_state)
{
BlockDriver *drv;

13
include/block/block_int-common.h
View File

@ -235,11 +235,14 @@ struct BlockDriver {
Error **errp);
/* For handling image reopen for split or non-split files. */
int (*bdrv_reopen_prepare)(BDRVReopenState *reopen_state,
BlockReopenQueue *queue, Error **errp);
void (*bdrv_reopen_commit)(BDRVReopenState *reopen_state);
void (*bdrv_reopen_commit_post)(BDRVReopenState *reopen_state);
void (*bdrv_reopen_abort)(BDRVReopenState *reopen_state);
int GRAPH_UNLOCKED_PTR (*bdrv_reopen_prepare)(
BDRVReopenState *reopen_state, BlockReopenQueue *queue, Error **errp);
void GRAPH_UNLOCKED_PTR (*bdrv_reopen_commit)(
BDRVReopenState *reopen_state);
void GRAPH_UNLOCKED_PTR (*bdrv_reopen_commit_post)(
BDRVReopenState *reopen_state);
void GRAPH_UNLOCKED_PTR (*bdrv_reopen_abort)(
BDRVReopenState *reopen_state);
void (*bdrv_join_options)(QDict *options, QDict *old_options);
int GRAPH_UNLOCKED_PTR (*bdrv_open)(