mirrors/qemu
0
0
Fork 0
mirror of https://github.com/qemu/qemu.git synced 2024-11-29 06:43:37 +08:00
Code Issues Packages Projects Releases Wiki Activity

block/vdi: Add locking for parallel requests

Browse Source 
When allocating a new cluster, the first write to it must be the one
doing the allocation, because that one pads its write request to the
cluster size; if another write to that cluster is executed before it,
that write will be overwritten due to the padding.

See https://bugs.launchpad.net/qemu/+bug/1422307 for what can go wrong
without this patch.

Cc: qemu-stable <qemu-stable@nongnu.org>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2015-02-27 14:54:39 -05:00 committed by Kevin Wolf
parent aef58bdc1e
commit f0ab6f1096
1 changed files with 25 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
block/vdi.c
View File

@ -53,6 +53,7 @@
#include "block/block_int.h"
#include "qemu/module.h"
#include "migration/migration.h"
#include "block/coroutine.h"
#if defined(CONFIG_UUID)
#include <uuid/uuid.h>
@ -196,6 +197,8 @@ typedef struct {
/* VDI header (converted to host endianness). */
VdiHeader header;
CoMutex write_lock;
Error *migration_blocker;
} BDRVVdiState;
@ -504,6 +507,8 @@ static int vdi_open(BlockDriverState *bs, QDict *options, int flags,
"vdi", bdrv_get_device_name(bs), "live migration");
migrate_add_blocker(s->migration_blocker);
qemu_co_mutex_init(&s->write_lock);
return 0;
fail_free_bmap:
@ -639,11 +644,31 @@ static int vdi_co_write(BlockDriverState *bs,
buf, n_sectors * SECTOR_SIZE);
memset(block + (sector_in_block + n_sectors) * SECTOR_SIZE, 0,
(s->block_sectors - n_sectors - sector_in_block) * SECTOR_SIZE);
/* Note that this coroutine does not yield anywhere from reading the
* bmap entry until here, so in regards to all the coroutines trying
* to write to this cluster, the one doing the allocation will
* always be the first to try to acquire the lock.
* Therefore, it is also the first that will actually be able to
* acquire the lock and thus the padded cluster is written before
* the other coroutines can write to the affected area. */
qemu_co_mutex_lock(&s->write_lock);
ret = bdrv_write(bs->file, offset, block, s->block_sectors);
qemu_co_mutex_unlock(&s->write_lock);
} else {
uint64_t offset = s->header.offset_data / SECTOR_SIZE +
(uint64_t)bmap_entry * s->block_sectors +
sector_in_block;
qemu_co_mutex_lock(&s->write_lock);
/* This lock is only used to make sure the following write operation
* is executed after the write issued by the coroutine allocating
* this cluster, therefore we do not need to keep it locked.
* As stated above, the allocating coroutine will always try to lock
* the mutex before all the other concurrent accesses to that
* cluster, therefore at this point we can be absolutely certain
* that that write operation has returned (there may be other writes
* in flight, but they do not concern this very operation). */
qemu_co_mutex_unlock(&s->write_lock);
ret = bdrv_write(bs->file, offset, buf, n_sectors);
}