* [PATCH v2 1/3] block: eliminate BDRV_REQ_NO_SERIALISING
2020-01-08 14:55 [PATCH v2 0/3] block/io: serialising request clean up and locking fix Paolo Bonzini
@ 2020-01-08 14:55 ` Paolo Bonzini
2020-01-08 14:55 ` [PATCH v2 2/3] block/io: wait for serialising requests when a request becomes serialising Paolo Bonzini
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Paolo Bonzini @ 2020-01-08 14:55 UTC (permalink / raw)
To: qemu-devel; +Cc: kwolf, qemu-block
It is unused since commit 00e30f0 ("block/backup: use backup-top instead
of write notifiers", 2019-10-01), drop it to simplify the code.
While at it, drop redundant assertions on flags.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
block/io.c | 18 ++++--------------
include/block/block.h | 12 ------------
2 files changed, 4 insertions(+), 26 deletions(-)
diff --git a/block/io.c b/block/io.c
index f75777f..b3a67fe 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1445,8 +1445,7 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
* potential fallback support, if we ever implement any read flags
* to pass through to drivers. For now, there aren't any
* passthrough flags. */
- assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ |
- BDRV_REQ_PREFETCH)));
+ assert(!(flags & ~(BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH)));
/* Handle Copy on Read and associated serialisation */
if (flags & BDRV_REQ_COPY_ON_READ) {
@@ -1458,12 +1457,7 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
bdrv_mark_request_serialising(req, bdrv_get_cluster_size(bs));
}
- /* BDRV_REQ_SERIALISING is only for write operation */
- assert(!(flags & BDRV_REQ_SERIALISING));
-
- if (!(flags & BDRV_REQ_NO_SERIALISING)) {
- bdrv_wait_serialising_requests(req);
- }
+ bdrv_wait_serialising_requests(req);
if (flags & BDRV_REQ_COPY_ON_READ) {
int64_t pnum;
@@ -1711,7 +1705,7 @@ int coroutine_fn bdrv_co_preadv_part(BdrvChild *child,
bdrv_inc_in_flight(bs);
/* Don't do copy-on-read if we read data before write operation */
- if (atomic_read(&bs->copy_on_read) && !(flags & BDRV_REQ_NO_SERIALISING)) {
+ if (atomic_read(&bs->copy_on_read)) {
flags |= BDRV_REQ_COPY_ON_READ;
}
@@ -1852,8 +1846,6 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes,
return -EPERM;
}
- /* BDRV_REQ_NO_SERIALISING is only for read operation */
- assert(!(flags & BDRV_REQ_NO_SERIALISING));
assert(!(bs->open_flags & BDRV_O_INACTIVE));
assert((bs->open_flags & BDRV_O_NO_IO) == 0);
assert(!(flags & ~BDRV_REQ_MASK));
@@ -3222,9 +3214,7 @@ static int coroutine_fn bdrv_co_copy_range_internal(
/* BDRV_REQ_SERIALISING is only for write operation */
assert(!(read_flags & BDRV_REQ_SERIALISING));
- if (!(read_flags & BDRV_REQ_NO_SERIALISING)) {
- bdrv_wait_serialising_requests(&req);
- }
+ bdrv_wait_serialising_requests(&req);
ret = src->bs->drv->bdrv_co_copy_range_from(src->bs,
src, src_offset,
diff --git a/include/block/block.h b/include/block/block.h
index e9dcfef..23c7642 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -51,18 +51,6 @@ typedef enum {
*/
BDRV_REQ_MAY_UNMAP = 0x4,
- /*
- * The BDRV_REQ_NO_SERIALISING flag is only valid for reads and means that
- * we don't want wait_serialising_requests() during the read operation.
- *
- * This flag is used for backup copy-on-write operations, when we need to
- * read old data before write (write notifier triggered). It is okay since
- * we already waited for other serializing requests in the initiating write
- * (see bdrv_aligned_pwritev), and it is necessary if the initiating write
- * is already serializing (without the flag, the read would deadlock
- * waiting for the serialising write to complete).
- */
- BDRV_REQ_NO_SERIALISING = 0x8,
BDRV_REQ_FUA = 0x10,
BDRV_REQ_WRITE_COMPRESSED = 0x20,
--
1.8.3.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH v2 2/3] block/io: wait for serialising requests when a request becomes serialising
2020-01-08 14:55 [PATCH v2 0/3] block/io: serialising request clean up and locking fix Paolo Bonzini
2020-01-08 14:55 ` [PATCH v2 1/3] block: eliminate BDRV_REQ_NO_SERIALISING Paolo Bonzini
@ 2020-01-08 14:55 ` Paolo Bonzini
2020-01-08 14:55 ` [PATCH v2 3/3] block/io: take bs->reqs_lock in bdrv_mark_request_serialising Paolo Bonzini
2020-01-14 16:28 ` [PATCH v2 0/3] block/io: serialising request clean up and locking fix Stefan Hajnoczi
3 siblings, 0 replies; 6+ messages in thread
From: Paolo Bonzini @ 2020-01-08 14:55 UTC (permalink / raw)
To: qemu-devel; +Cc: kwolf, qemu-block
Marking without waiting would not result in actual serialising behavior.
Thus, make a call bdrv_mark_request_serialising sufficient for
serialisation to happen.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
block/file-posix.c | 1 -
block/io.c | 40 +++++++++++++++++-----------------------
include/block/block_int.h | 3 +--
3 files changed, 18 insertions(+), 26 deletions(-)
diff --git a/block/file-posix.c b/block/file-posix.c
index 1b805bd..2b08b02 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2753,7 +2753,6 @@ raw_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int bytes,
req->overlap_bytes = req->bytes;
bdrv_mark_request_serialising(req, bs->bl.request_alignment);
- bdrv_wait_serialising_requests(req);
}
#endif
diff --git a/block/io.c b/block/io.c
index b3a67fe..c466df8 100644
--- a/block/io.c
+++ b/block/io.c
@@ -41,6 +41,7 @@
#define MAX_BOUNCE_BUFFER (32768 << BDRV_SECTOR_BITS)
static void bdrv_parent_cb_resize(BlockDriverState *bs);
+static bool coroutine_fn bdrv_wait_serialising_requests(BdrvTrackedRequest *self);
static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
int64_t offset, int bytes, BdrvRequestFlags flags);
@@ -715,7 +716,7 @@ static void tracked_request_begin(BdrvTrackedRequest *req,
qemu_co_mutex_unlock(&bs->reqs_lock);
}
-void bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align)
+bool bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align)
{
int64_t overlap_offset = req->offset & ~(align - 1);
uint64_t overlap_bytes = ROUND_UP(req->offset + req->bytes, align)
@@ -728,18 +729,7 @@ void bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align)
req->overlap_offset = MIN(req->overlap_offset, overlap_offset);
req->overlap_bytes = MAX(req->overlap_bytes, overlap_bytes);
-}
-
-static bool is_request_serialising_and_aligned(BdrvTrackedRequest *req)
-{
- /*
- * If the request is serialising, overlap_offset and overlap_bytes are set,
- * so we can check if the request is aligned. Otherwise, don't care and
- * return false.
- */
-
- return req->serialising && (req->offset == req->overlap_offset) &&
- (req->bytes == req->overlap_bytes);
+ return bdrv_wait_serialising_requests(req);
}
/**
@@ -823,7 +813,7 @@ void bdrv_dec_in_flight(BlockDriverState *bs)
bdrv_wakeup(bs);
}
-bool coroutine_fn bdrv_wait_serialising_requests(BdrvTrackedRequest *self)
+static bool coroutine_fn bdrv_wait_serialising_requests(BdrvTrackedRequest *self)
{
BlockDriverState *bs = self->bs;
BdrvTrackedRequest *req;
@@ -1455,10 +1445,10 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
* it ensures that the CoR read and write operations are atomic and
* guest writes cannot interleave between them. */
bdrv_mark_request_serialising(req, bdrv_get_cluster_size(bs));
+ } else {
+ bdrv_wait_serialising_requests(req);
}
- bdrv_wait_serialising_requests(req);
-
if (flags & BDRV_REQ_COPY_ON_READ) {
int64_t pnum;
@@ -1851,13 +1841,19 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, uint64_t bytes,
assert(!(flags & ~BDRV_REQ_MASK));
if (flags & BDRV_REQ_SERIALISING) {
- bdrv_mark_request_serialising(req, bdrv_get_cluster_size(bs));
+ waited = bdrv_mark_request_serialising(req, bdrv_get_cluster_size(bs));
+ /*
+ * For a misaligned request we should have already waited earlier,
+ * because we come after bdrv_padding_rmw_read which must be called
+ * with the request already marked as serialising.
+ */
+ assert(!waited ||
+ (req->offset == req->overlap_offset &&
+ req->bytes == req->overlap_bytes));
+ } else {
+ bdrv_wait_serialising_requests(req);
}
- waited = bdrv_wait_serialising_requests(req);
-
- assert(!waited || !req->serialising ||
- is_request_serialising_and_aligned(req));
assert(req->overlap_offset <= offset);
assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
assert(end_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE);
@@ -2019,7 +2015,6 @@ static int coroutine_fn bdrv_co_do_zero_pwritev(BdrvChild *child,
padding = bdrv_init_padding(bs, offset, bytes, &pad);
if (padding) {
bdrv_mark_request_serialising(req, align);
- bdrv_wait_serialising_requests(req);
bdrv_padding_rmw_read(child, req, &pad, true);
@@ -2122,7 +2117,6 @@ int coroutine_fn bdrv_co_pwritev_part(BdrvChild *child,
if (bdrv_pad_request(bs, &qiov, &qiov_offset, &offset, &bytes, &pad)) {
bdrv_mark_request_serialising(&req, align);
- bdrv_wait_serialising_requests(&req);
bdrv_padding_rmw_read(child, &req, &pad, false);
}
diff --git a/include/block/block_int.h b/include/block/block_int.h
index dd033d0..640fb82 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -999,8 +999,7 @@ extern unsigned int bdrv_drain_all_count;
void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent);
void bdrv_unapply_subtree_drain(BdrvChild *child, BlockDriverState *old_parent);
-bool coroutine_fn bdrv_wait_serialising_requests(BdrvTrackedRequest *self);
-void bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align);
+bool coroutine_fn bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align);
BdrvTrackedRequest *coroutine_fn bdrv_co_get_self_request(BlockDriverState *bs);
int get_tmp_filename(char *filename, int size);
--
1.8.3.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH v2 3/3] block/io: take bs->reqs_lock in bdrv_mark_request_serialising
2020-01-08 14:55 [PATCH v2 0/3] block/io: serialising request clean up and locking fix Paolo Bonzini
2020-01-08 14:55 ` [PATCH v2 1/3] block: eliminate BDRV_REQ_NO_SERIALISING Paolo Bonzini
2020-01-08 14:55 ` [PATCH v2 2/3] block/io: wait for serialising requests when a request becomes serialising Paolo Bonzini
@ 2020-01-08 14:55 ` Paolo Bonzini
2020-01-14 16:28 ` [PATCH v2 0/3] block/io: serialising request clean up and locking fix Stefan Hajnoczi
3 siblings, 0 replies; 6+ messages in thread
From: Paolo Bonzini @ 2020-01-08 14:55 UTC (permalink / raw)
To: qemu-devel; +Cc: kwolf, qemu-block
bdrv_mark_request_serialising is writing the overlap_offset and
overlap_bytes fields of BdrvTrackedRequest. Take bs->reqs_lock
for the whole duration of it, and not just when waiting for
serialising requests, so that tracked_request_overlaps does not
look at a half-updated request.
The new code does not unlock/relock around retries. This is unnecessary
because a retry is always preceded by a CoQueue wait, which already
releases and reacquires bs->reqs_lock.
Reported-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
block/io.c | 112 ++++++++++++++++++++++++++++++++++---------------------------
1 file changed, 63 insertions(+), 49 deletions(-)
diff --git a/block/io.c b/block/io.c
index c466df8..1eb2b2b 100644
--- a/block/io.c
+++ b/block/io.c
@@ -41,7 +41,6 @@
#define MAX_BOUNCE_BUFFER (32768 << BDRV_SECTOR_BITS)
static void bdrv_parent_cb_resize(BlockDriverState *bs);
-static bool coroutine_fn bdrv_wait_serialising_requests(BdrvTrackedRequest *self);
static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
int64_t offset, int bytes, BdrvRequestFlags flags);
@@ -716,12 +715,69 @@ static void tracked_request_begin(BdrvTrackedRequest *req,
qemu_co_mutex_unlock(&bs->reqs_lock);
}
+static bool tracked_request_overlaps(BdrvTrackedRequest *req,
+ int64_t offset, uint64_t bytes)
+{
+ /* aaaa bbbb */
+ if (offset >= req->overlap_offset + req->overlap_bytes) {
+ return false;
+ }
+ /* bbbb aaaa */
+ if (req->overlap_offset >= offset + bytes) {
+ return false;
+ }
+ return true;
+}
+
+static bool coroutine_fn
+bdrv_wait_serialising_requests_locked(BlockDriverState *bs,
+ BdrvTrackedRequest *self)
+{
+ BdrvTrackedRequest *req;
+ bool retry;
+ bool waited = false;
+
+ do {
+ retry = false;
+ QLIST_FOREACH(req, &bs->tracked_requests, list) {
+ if (req == self || (!req->serialising && !self->serialising)) {
+ continue;
+ }
+ if (tracked_request_overlaps(req, self->overlap_offset,
+ self->overlap_bytes))
+ {
+ /* Hitting this means there was a reentrant request, for
+ * example, a block driver issuing nested requests. This must
+ * never happen since it means deadlock.
+ */
+ assert(qemu_coroutine_self() != req->co);
+
+ /* If the request is already (indirectly) waiting for us, or
+ * will wait for us as soon as it wakes up, then just go on
+ * (instead of producing a deadlock in the former case). */
+ if (!req->waiting_for) {
+ self->waiting_for = req;
+ qemu_co_queue_wait(&req->wait_queue, &bs->reqs_lock);
+ self->waiting_for = NULL;
+ retry = true;
+ waited = true;
+ break;
+ }
+ }
+ }
+ } while (retry);
+ return waited;
+}
+
bool bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align)
{
+ BlockDriverState *bs = req->bs;
int64_t overlap_offset = req->offset & ~(align - 1);
uint64_t overlap_bytes = ROUND_UP(req->offset + req->bytes, align)
- overlap_offset;
+ bool waited;
+ qemu_co_mutex_lock(&bs->reqs_lock);
if (!req->serialising) {
atomic_inc(&req->bs->serialising_in_flight);
req->serialising = true;
@@ -729,7 +785,9 @@ bool bdrv_mark_request_serialising(BdrvTrackedRequest *req, uint64_t align)
req->overlap_offset = MIN(req->overlap_offset, overlap_offset);
req->overlap_bytes = MAX(req->overlap_bytes, overlap_bytes);
- return bdrv_wait_serialising_requests(req);
+ waited = bdrv_wait_serialising_requests_locked(bs, req);
+ qemu_co_mutex_unlock(&bs->reqs_lock);
+ return waited;
}
/**
@@ -783,20 +841,6 @@ static int bdrv_get_cluster_size(BlockDriverState *bs)
}
}
-static bool tracked_request_overlaps(BdrvTrackedRequest *req,
- int64_t offset, uint64_t bytes)
-{
- /* aaaa bbbb */
- if (offset >= req->overlap_offset + req->overlap_bytes) {
- return false;
- }
- /* bbbb aaaa */
- if (req->overlap_offset >= offset + bytes) {
- return false;
- }
- return true;
-}
-
void bdrv_inc_in_flight(BlockDriverState *bs)
{
atomic_inc(&bs->in_flight);
@@ -816,45 +860,15 @@ void bdrv_dec_in_flight(BlockDriverState *bs)
static bool coroutine_fn bdrv_wait_serialising_requests(BdrvTrackedRequest *self)
{
BlockDriverState *bs = self->bs;
- BdrvTrackedRequest *req;
- bool retry;
bool waited = false;
if (!atomic_read(&bs->serialising_in_flight)) {
return false;
}
- do {
- retry = false;
- qemu_co_mutex_lock(&bs->reqs_lock);
- QLIST_FOREACH(req, &bs->tracked_requests, list) {
- if (req == self || (!req->serialising && !self->serialising)) {
- continue;
- }
- if (tracked_request_overlaps(req, self->overlap_offset,
- self->overlap_bytes))
- {
- /* Hitting this means there was a reentrant request, for
- * example, a block driver issuing nested requests. This must
- * never happen since it means deadlock.
- */
- assert(qemu_coroutine_self() != req->co);
-
- /* If the request is already (indirectly) waiting for us, or
- * will wait for us as soon as it wakes up, then just go on
- * (instead of producing a deadlock in the former case). */
- if (!req->waiting_for) {
- self->waiting_for = req;
- qemu_co_queue_wait(&req->wait_queue, &bs->reqs_lock);
- self->waiting_for = NULL;
- retry = true;
- waited = true;
- break;
- }
- }
- }
- qemu_co_mutex_unlock(&bs->reqs_lock);
- } while (retry);
+ qemu_co_mutex_lock(&bs->reqs_lock);
+ waited = bdrv_wait_serialising_requests_locked(bs, self);
+ qemu_co_mutex_unlock(&bs->reqs_lock);
return waited;
}
--
1.8.3.1
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v2 0/3] block/io: serialising request clean up and locking fix
2020-01-08 14:55 [PATCH v2 0/3] block/io: serialising request clean up and locking fix Paolo Bonzini
` (2 preceding siblings ...)
2020-01-08 14:55 ` [PATCH v2 3/3] block/io: take bs->reqs_lock in bdrv_mark_request_serialising Paolo Bonzini
@ 2020-01-14 16:28 ` Stefan Hajnoczi
2020-01-14 19:39 ` Paolo Bonzini
3 siblings, 1 reply; 6+ messages in thread
From: Stefan Hajnoczi @ 2020-01-14 16:28 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: kwolf, qemu-devel, qemu-block
[-- Attachment #1: Type: text/plain, Size: 980 bytes --]
On Wed, Jan 08, 2020 at 03:55:53PM +0100, Paolo Bonzini wrote:
> Peter Lieven noticed that reqs->overlap_offset and reqs->overlap_bytes
> are written outside bs->reqs_lock. Patch 3 fixes it, while patches 1
> and 2 are preparatory cleanups.
>
> v1->v2: fix comment in patch 2, commit message in patch 3 [Kevin]
>
> Paolo Bonzini (3):
> block: eliminate BDRV_REQ_NO_SERIALISING
> block/io: wait for serialising requests when a request becomes
> serialising
> block/io: take bs->reqs_lock in bdrv_mark_request_serialising
>
> block/file-posix.c | 1 -
> block/io.c | 162 +++++++++++++++++++++++-----------------------
> include/block/block.h | 12 ----
> include/block/block_int.h | 3 +-
> 4 files changed, 81 insertions(+), 97 deletions(-)
Is it possible to trigger the bug somehow?
Can you implement a test case?
Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block
Stefan
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2 0/3] block/io: serialising request clean up and locking fix
2020-01-14 16:28 ` [PATCH v2 0/3] block/io: serialising request clean up and locking fix Stefan Hajnoczi
@ 2020-01-14 19:39 ` Paolo Bonzini
0 siblings, 0 replies; 6+ messages in thread
From: Paolo Bonzini @ 2020-01-14 19:39 UTC (permalink / raw)
To: Stefan Hajnoczi; +Cc: kwolf, qemu-devel, qemu-block
[-- Attachment #1.1: Type: text/plain, Size: 1060 bytes --]
On 14/01/20 17:28, Stefan Hajnoczi wrote:
> On Wed, Jan 08, 2020 at 03:55:53PM +0100, Paolo Bonzini wrote:
>> Peter Lieven noticed that reqs->overlap_offset and reqs->overlap_bytes
>> are written outside bs->reqs_lock. Patch 3 fixes it, while patches 1
>> and 2 are preparatory cleanups.
>>
>> v1->v2: fix comment in patch 2, commit message in patch 3 [Kevin]
>>
>> Paolo Bonzini (3):
>> block: eliminate BDRV_REQ_NO_SERIALISING
>> block/io: wait for serialising requests when a request becomes
>> serialising
>> block/io: take bs->reqs_lock in bdrv_mark_request_serialising
>>
>> block/file-posix.c | 1 -
>> block/io.c | 162 +++++++++++++++++++++++-----------------------
>> include/block/block.h | 12 ----
>> include/block/block_int.h | 3 +-
>> 4 files changed, 81 insertions(+), 97 deletions(-)
> Is it possible to trigger the bug somehow?
>
> Can you implement a test case?
No, it was found by inspection only, and it's actually protected by the
AioContext lock for now.
Paolo
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread