qemu/block/backup.c
Sergio Lopez 0abf258171 block/backup-top: Don't acquire context while dropping top
All paths that lead to bdrv_backup_top_drop(), except for the call
from backup_clean(), imply that the BDS AioContext has already been
acquired, so doing it there too can potentially lead to QEMU hanging
on AIO_WAIT_WHILE().

An easy way to trigger this situation is by issuing a two actions
transaction, with a proper and a bogus blockdev-backup, so the second
one will trigger a rollback. This will trigger a hang with an stack
trace like this one:

 #0  0x00007fb680c75016 in __GI_ppoll (fds=0x55e74580f7c0, nfds=1, timeout=<optimized out>,
     timeout@entry=0x0, sigmask=sigmask@entry=0x0) at ../sysdeps/unix/sysv/linux/ppoll.c:39
 #1  0x000055e743386e09 in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized out>, __fds=<optimized out>)
     at /usr/include/bits/poll2.h:77
 #2  0x000055e743386e09 in qemu_poll_ns
     (fds=<optimized out>, nfds=<optimized out>, timeout=<optimized out>) at util/qemu-timer.c:336
 #3  0x000055e743388dc4 in aio_poll (ctx=0x55e7458925d0, blocking=blocking@entry=true)
     at util/aio-posix.c:669
 #4  0x000055e743305dea in bdrv_flush (bs=bs@entry=0x55e74593c0d0) at block/io.c:2878
 #5  0x000055e7432be58e in bdrv_close (bs=0x55e74593c0d0) at block.c:4017
 #6  0x000055e7432be58e in bdrv_delete (bs=<optimized out>) at block.c:4262
 #7  0x000055e7432be58e in bdrv_unref (bs=bs@entry=0x55e74593c0d0) at block.c:5644
 #8  0x000055e743316b9b in bdrv_backup_top_drop (bs=bs@entry=0x55e74593c0d0) at block/backup-top.c:273
 #9  0x000055e74331461f in backup_job_create
     (job_id=0x0, bs=bs@entry=0x55e7458d5820, target=target@entry=0x55e74589f640, speed=0, sync_mode=MIRROR_SYNC_MODE_FULL, sync_bitmap=sync_bitmap@entry=0x0, bitmap_mode=BITMAP_SYNC_MODE_ON_SUCCESS, compress=false, filter_node_name=0x0, on_source_error=BLOCKDEV_ON_ERROR_REPORT, on_target_error=BLOCKDEV_ON_ERROR_REPORT, creation_flags=0, cb=0x0, opaque=0x0, txn=0x0, errp=0x7ffddfd1efb0) at block/backup.c:478
 #10 0x000055e74315bc52 in do_backup_common
     (backup=backup@entry=0x55e746c066d0, bs=bs@entry=0x55e7458d5820, target_bs=target_bs@entry=0x55e74589f640, aio_context=aio_context@entry=0x55e7458a91e0, txn=txn@entry=0x0, errp=errp@entry=0x7ffddfd1efb0)
     at blockdev.c:3580
 #11 0x000055e74315c37c in do_blockdev_backup
     (backup=backup@entry=0x55e746c066d0, txn=0x0, errp=errp@entry=0x7ffddfd1efb0)
     at /usr/src/debug/qemu-kvm-4.2.0-2.module+el8.2.0+5135+ed3b2489.x86_64/./qapi/qapi-types-block-core.h:1492
 #12 0x000055e74315c449 in blockdev_backup_prepare (common=0x55e746a8de90, errp=0x7ffddfd1f018)
     at blockdev.c:1885
 #13 0x000055e743160152 in qmp_transaction
     (dev_list=<optimized out>, has_props=<optimized out>, props=0x55e7467fe2c0, errp=errp@entry=0x7ffddfd1f088) at blockdev.c:2340
 #14 0x000055e743287ff5 in qmp_marshal_transaction
     (args=<optimized out>, ret=<optimized out>, errp=0x7ffddfd1f0f8)
     at qapi/qapi-commands-transaction.c:44
 #15 0x000055e74333de6c in do_qmp_dispatch
     (errp=0x7ffddfd1f0f0, allow_oob=<optimized out>, request=<optimized out>, cmds=0x55e743c28d60 <qmp_commands>) at qapi/qmp-dispatch.c:132
 #16 0x000055e74333de6c in qmp_dispatch
     (cmds=0x55e743c28d60 <qmp_commands>, request=<optimized out>, allow_oob=<optimized out>)
     at qapi/qmp-dispatch.c:175
 #17 0x000055e74325c061 in monitor_qmp_dispatch (mon=0x55e745908030, req=<optimized out>)
     at monitor/qmp.c:145
 #18 0x000055e74325c6fa in monitor_qmp_bh_dispatcher (data=<optimized out>) at monitor/qmp.c:234
 #19 0x000055e743385866 in aio_bh_call (bh=0x55e745807ae0) at util/async.c:117
 #20 0x000055e743385866 in aio_bh_poll (ctx=ctx@entry=0x55e7458067a0) at util/async.c:117
 #21 0x000055e743388c54 in aio_dispatch (ctx=0x55e7458067a0) at util/aio-posix.c:459
 #22 0x000055e743385742 in aio_ctx_dispatch
     (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at util/async.c:260
 #23 0x00007fb68543e67d in g_main_dispatch (context=0x55e745893a40) at gmain.c:3176
 #24 0x00007fb68543e67d in g_main_context_dispatch (context=context@entry=0x55e745893a40) at gmain.c:3829
 #25 0x000055e743387d08 in glib_pollfds_poll () at util/main-loop.c:219
 #26 0x000055e743387d08 in os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:242
 #27 0x000055e743387d08 in main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:518
 #28 0x000055e74316a3c1 in main_loop () at vl.c:1828
 #29 0x000055e743016a72 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>)
     at vl.c:4504

Fix this by not acquiring the AioContext there, and ensuring all paths
leading to it have it already acquired (backup_clean()).

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1782111
Signed-off-by: Sergio Lopez <slp@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2020-01-27 17:19:53 +01:00

486 lines
14 KiB
C

/*
* QEMU backup
*
* Copyright (C) 2013 Proxmox Server Solutions
* Copyright (c) 2019 Virtuozzo International GmbH.
*
* Authors:
* Dietmar Maurer (dietmar@proxmox.com)
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "block/block.h"
#include "block/block_int.h"
#include "block/blockjob_int.h"
#include "block/block_backup.h"
#include "block/block-copy.h"
#include "qapi/error.h"
#include "qapi/qmp/qerror.h"
#include "qemu/ratelimit.h"
#include "qemu/cutils.h"
#include "sysemu/block-backend.h"
#include "qemu/bitmap.h"
#include "qemu/error-report.h"
#include "block/backup-top.h"
#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
typedef struct BackupBlockJob {
BlockJob common;
BlockDriverState *backup_top;
BlockDriverState *source_bs;
BdrvDirtyBitmap *sync_bitmap;
MirrorSyncMode sync_mode;
BitmapSyncMode bitmap_mode;
BlockdevOnError on_source_error;
BlockdevOnError on_target_error;
uint64_t len;
uint64_t bytes_read;
int64_t cluster_size;
BlockCopyState *bcs;
} BackupBlockJob;
static const BlockJobDriver backup_job_driver;
static void backup_progress_bytes_callback(int64_t bytes, void *opaque)
{
BackupBlockJob *s = opaque;
s->bytes_read += bytes;
job_progress_update(&s->common.job, bytes);
}
static void backup_progress_reset_callback(void *opaque)
{
BackupBlockJob *s = opaque;
uint64_t estimate = bdrv_get_dirty_count(s->bcs->copy_bitmap);
job_progress_set_remaining(&s->common.job, estimate);
}
static int coroutine_fn backup_do_cow(BackupBlockJob *job,
int64_t offset, uint64_t bytes,
bool *error_is_read)
{
int ret = 0;
int64_t start, end; /* bytes */
start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
trace_backup_do_cow_enter(job, start, offset, bytes);
ret = block_copy(job->bcs, start, end - start, error_is_read);
trace_backup_do_cow_return(job, offset, bytes, ret);
return ret;
}
static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
{
BdrvDirtyBitmap *bm;
bool sync = (((ret == 0) || (job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS)) \
&& (job->bitmap_mode != BITMAP_SYNC_MODE_NEVER));
if (sync) {
/*
* We succeeded, or we always intended to sync the bitmap.
* Delete this bitmap and install the child.
*/
bm = bdrv_dirty_bitmap_abdicate(job->sync_bitmap, NULL);
} else {
/*
* We failed, or we never intended to sync the bitmap anyway.
* Merge the successor back into the parent, keeping all data.
*/
bm = bdrv_reclaim_dirty_bitmap(job->sync_bitmap, NULL);
}
assert(bm);
if (ret < 0 && job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS) {
/* If we failed and synced, merge in the bits we didn't copy: */
bdrv_dirty_bitmap_merge_internal(bm, job->bcs->copy_bitmap,
NULL, true);
}
}
static void backup_commit(Job *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
if (s->sync_bitmap) {
backup_cleanup_sync_bitmap(s, 0);
}
}
static void backup_abort(Job *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
if (s->sync_bitmap) {
backup_cleanup_sync_bitmap(s, -1);
}
}
static void backup_clean(Job *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
AioContext *aio_context = bdrv_get_aio_context(s->backup_top);
aio_context_acquire(aio_context);
bdrv_backup_top_drop(s->backup_top);
aio_context_release(aio_context);
}
void backup_do_checkpoint(BlockJob *job, Error **errp)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
assert(block_job_driver(job) == &backup_job_driver);
if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
error_setg(errp, "The backup job only supports block checkpoint in"
" sync=none mode");
return;
}
bdrv_set_dirty_bitmap(backup_job->bcs->copy_bitmap, 0, backup_job->len);
}
static BlockErrorAction backup_error_action(BackupBlockJob *job,
bool read, int error)
{
if (read) {
return block_job_error_action(&job->common, job->on_source_error,
true, error);
} else {
return block_job_error_action(&job->common, job->on_target_error,
false, error);
}
}
static bool coroutine_fn yield_and_check(BackupBlockJob *job)
{
uint64_t delay_ns;
if (job_is_cancelled(&job->common.job)) {
return true;
}
/*
* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
* return. Without a yield, the VM would not reboot.
*/
delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
job->bytes_read = 0;
job_sleep_ns(&job->common.job, delay_ns);
if (job_is_cancelled(&job->common.job)) {
return true;
}
return false;
}
static int coroutine_fn backup_loop(BackupBlockJob *job)
{
bool error_is_read;
int64_t offset;
BdrvDirtyBitmapIter *bdbi;
int ret = 0;
bdbi = bdrv_dirty_iter_new(job->bcs->copy_bitmap);
while ((offset = bdrv_dirty_iter_next(bdbi)) != -1) {
do {
if (yield_and_check(job)) {
goto out;
}
ret = backup_do_cow(job, offset, job->cluster_size, &error_is_read);
if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
BLOCK_ERROR_ACTION_REPORT)
{
goto out;
}
} while (ret < 0);
}
out:
bdrv_dirty_iter_free(bdbi);
return ret;
}
static void backup_init_copy_bitmap(BackupBlockJob *job)
{
bool ret;
uint64_t estimate;
if (job->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
ret = bdrv_dirty_bitmap_merge_internal(job->bcs->copy_bitmap,
job->sync_bitmap,
NULL, true);
assert(ret);
} else {
if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
/*
* We can't hog the coroutine to initialize this thoroughly.
* Set a flag and resume work when we are able to yield safely.
*/
job->bcs->skip_unallocated = true;
}
bdrv_set_dirty_bitmap(job->bcs->copy_bitmap, 0, job->len);
}
estimate = bdrv_get_dirty_count(job->bcs->copy_bitmap);
job_progress_set_remaining(&job->common.job, estimate);
}
static int coroutine_fn backup_run(Job *job, Error **errp)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
int ret = 0;
backup_init_copy_bitmap(s);
if (s->sync_mode == MIRROR_SYNC_MODE_TOP) {
int64_t offset = 0;
int64_t count;
for (offset = 0; offset < s->len; ) {
if (yield_and_check(s)) {
ret = -ECANCELED;
goto out;
}
ret = block_copy_reset_unallocated(s->bcs, offset, &count);
if (ret < 0) {
goto out;
}
offset += count;
}
s->bcs->skip_unallocated = false;
}
if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
/*
* All bits are set in copy_bitmap to allow any cluster to be copied.
* This does not actually require them to be copied.
*/
while (!job_is_cancelled(job)) {
/*
* Yield until the job is cancelled. We just let our before_write
* notify callback service CoW requests.
*/
job_yield(job);
}
} else {
ret = backup_loop(s);
}
out:
return ret;
}
static const BlockJobDriver backup_job_driver = {
.job_driver = {
.instance_size = sizeof(BackupBlockJob),
.job_type = JOB_TYPE_BACKUP,
.free = block_job_free,
.user_resume = block_job_user_resume,
.run = backup_run,
.commit = backup_commit,
.abort = backup_abort,
.clean = backup_clean,
}
};
static int64_t backup_calculate_cluster_size(BlockDriverState *target,
Error **errp)
{
int ret;
BlockDriverInfo bdi;
/*
* If there is no backing file on the target, we cannot rely on COW if our
* backup cluster size is smaller than the target cluster size. Even for
* targets with a backing file, try to avoid COW if possible.
*/
ret = bdrv_get_info(target, &bdi);
if (ret == -ENOTSUP && !target->backing) {
/* Cluster size is not defined */
warn_report("The target block device doesn't provide "
"information about the block size and it doesn't have a "
"backing file. The default block size of %u bytes is "
"used. If the actual block size of the target exceeds "
"this default, the backup may be unusable",
BACKUP_CLUSTER_SIZE_DEFAULT);
return BACKUP_CLUSTER_SIZE_DEFAULT;
} else if (ret < 0 && !target->backing) {
error_setg_errno(errp, -ret,
"Couldn't determine the cluster size of the target image, "
"which has no backing file");
error_append_hint(errp,
"Aborting, since this may create an unusable destination image\n");
return ret;
} else if (ret < 0 && target->backing) {
/* Not fatal; just trudge on ahead. */
return BACKUP_CLUSTER_SIZE_DEFAULT;
}
return MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
}
BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
BlockDriverState *target, int64_t speed,
MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
BitmapSyncMode bitmap_mode,
bool compress,
const char *filter_node_name,
BlockdevOnError on_source_error,
BlockdevOnError on_target_error,
int creation_flags,
BlockCompletionFunc *cb, void *opaque,
JobTxn *txn, Error **errp)
{
int64_t len;
BackupBlockJob *job = NULL;
int64_t cluster_size;
BdrvRequestFlags write_flags;
BlockDriverState *backup_top = NULL;
BlockCopyState *bcs = NULL;
assert(bs);
assert(target);
/* QMP interface protects us from these cases */
assert(sync_mode != MIRROR_SYNC_MODE_INCREMENTAL);
assert(sync_bitmap || sync_mode != MIRROR_SYNC_MODE_BITMAP);
if (bs == target) {
error_setg(errp, "Source and target cannot be the same");
return NULL;
}
if (!bdrv_is_inserted(bs)) {
error_setg(errp, "Device is not inserted: %s",
bdrv_get_device_name(bs));
return NULL;
}
if (!bdrv_is_inserted(target)) {
error_setg(errp, "Device is not inserted: %s",
bdrv_get_device_name(target));
return NULL;
}
if (compress && !block_driver_can_compress(target->drv)) {
error_setg(errp, "Compression is not supported for this drive %s",
bdrv_get_device_name(target));
return NULL;
}
if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
return NULL;
}
if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
return NULL;
}
if (sync_bitmap) {
/* If we need to write to this bitmap, check that we can: */
if (bitmap_mode != BITMAP_SYNC_MODE_NEVER &&
bdrv_dirty_bitmap_check(sync_bitmap, BDRV_BITMAP_DEFAULT, errp)) {
return NULL;
}
/* Create a new bitmap, and freeze/disable this one. */
if (bdrv_dirty_bitmap_create_successor(sync_bitmap, errp) < 0) {
return NULL;
}
}
len = bdrv_getlength(bs);
if (len < 0) {
error_setg_errno(errp, -len, "unable to get length for '%s'",
bdrv_get_device_name(bs));
goto error;
}
cluster_size = backup_calculate_cluster_size(target, errp);
if (cluster_size < 0) {
goto error;
}
/*
* If source is in backing chain of target assume that target is going to be
* used for "image fleecing", i.e. it should represent a kind of snapshot of
* source at backup-start point in time. And target is going to be read by
* somebody (for example, used as NBD export) during backup job.
*
* In this case, we need to add BDRV_REQ_SERIALISING write flag to avoid
* intersection of backup writes and third party reads from target,
* otherwise reading from target we may occasionally read already updated by
* guest data.
*
* For more information see commit f8d59dfb40bb and test
* tests/qemu-iotests/222
*/
write_flags = (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
(compress ? BDRV_REQ_WRITE_COMPRESSED : 0),
backup_top = bdrv_backup_top_append(bs, target, filter_node_name,
cluster_size, write_flags, &bcs, errp);
if (!backup_top) {
goto error;
}
/* job->len is fixed, so we can't allow resize */
job = block_job_create(job_id, &backup_job_driver, txn, backup_top,
0, BLK_PERM_ALL,
speed, creation_flags, cb, opaque, errp);
if (!job) {
goto error;
}
job->backup_top = backup_top;
job->source_bs = bs;
job->on_source_error = on_source_error;
job->on_target_error = on_target_error;
job->sync_mode = sync_mode;
job->sync_bitmap = sync_bitmap;
job->bitmap_mode = bitmap_mode;
job->bcs = bcs;
job->cluster_size = cluster_size;
job->len = len;
block_copy_set_callbacks(bcs, backup_progress_bytes_callback,
backup_progress_reset_callback, job);
/* Required permissions are already taken by backup-top target */
block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
&error_abort);
return &job->common;
error:
if (sync_bitmap) {
bdrv_reclaim_dirty_bitmap(sync_bitmap, NULL);
}
if (backup_top) {
bdrv_backup_top_drop(backup_top);
}
return NULL;
}