[Qemu-devel] [PATCH] block: bdrv_invalidate_cache: invalidate children first

[Qemu-devel] [PATCH] block: bdrv_invalidate_cache: invalidate children first

[Vladimir Sementsov-Ogievskiy]

Current implementation invalidates firstly parent bds and then its
children. This leads to the following bug:

after incoming migration, in bdrv_invalidate_cache_all:
1. invalidate parent bds - reopen it with BDRV_O_INACTIVE cleared
2. child is not yet invalidated
3. parent check that its BDRV_O_INACTIVE is cleared
4. parent writes to child
5. assert in bdrv_co_pwritev, as BDRV_O_INACTIVE is set for child

This patch fixes it by just changing invalidate sequence: invalidate
children first.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

v2: I've missed that bdrv_invalidate_cache is already recursive, so we
can change sequence here. Also v1 doesn't cover the case when
bdrv_invalidate_cache is called not from bdrv_invalidate_cache_all.

 block.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/block.c b/block.c
index a0346c80c6..dce1dc02af 100644
--- a/block.c
+++ b/block.c
@@ -3235,19 +3235,18 @@ void bdrv_invalidate_cache(BlockDriverState *bs, Error **errp)
     if (!(bs->open_flags & BDRV_O_INACTIVE)) {
         return;
     }
-    bs->open_flags &= ~BDRV_O_INACTIVE;
 
-    if (bs->drv->bdrv_invalidate_cache) {
-        bs->drv->bdrv_invalidate_cache(bs, &local_err);
+    QLIST_FOREACH(child, &bs->children, next) {
+        bdrv_invalidate_cache(child->bs, &local_err);
         if (local_err) {
-            bs->open_flags |= BDRV_O_INACTIVE;
             error_propagate(errp, local_err);
             return;
         }
     }
 
-    QLIST_FOREACH(child, &bs->children, next) {
-        bdrv_invalidate_cache(child->bs, &local_err);
+    bs->open_flags &= ~BDRV_O_INACTIVE;
+    if (bs->drv->bdrv_invalidate_cache) {
+        bs->drv->bdrv_invalidate_cache(bs, &local_err);
         if (local_err) {
             bs->open_flags |= BDRV_O_INACTIVE;
             error_propagate(errp, local_err);
-- 
2.11.0

Re: [Qemu-devel] [PATCH] block: bdrv_invalidate_cache: invalidate children first

[Vladimir Sementsov-Ogievskiy]

v2 missed in topic, sorry for that.

First version was "[PATCH] block: bdrv_invalidate_cache_all: invalidate 
children first"

-- 
Best regards,
Vladimir

Re: [Qemu-devel] [PATCH] block: bdrv_invalidate_cache: invalidate children first

[Max Reitz]

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On 31.01.2017 12:23, Vladimir Sementsov-Ogievskiy wrote:
> Current implementation invalidates firstly parent bds and then its
> children. This leads to the following bug:
> 
> after incoming migration, in bdrv_invalidate_cache_all:
> 1. invalidate parent bds - reopen it with BDRV_O_INACTIVE cleared
> 2. child is not yet invalidated
> 3. parent check that its BDRV_O_INACTIVE is cleared
> 4. parent writes to child
> 5. assert in bdrv_co_pwritev, as BDRV_O_INACTIVE is set for child
> 
> This patch fixes it by just changing invalidate sequence: invalidate
> children first.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> v2: I've missed that bdrv_invalidate_cache is already recursive, so we
> can change sequence here. Also v1 doesn't cover the case when
> bdrv_invalidate_cache is called not from bdrv_invalidate_cache_all.
> 
>  block.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>

I'll wait a bit until I apply this patch (please remind me next week if
I forget it...), though, because migration-related things are not
exactly my forte, so maybe someone else has something to say.

Max


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Re: [Qemu-devel] [PATCH] block: bdrv_invalidate_cache: invalidate children first

[Stefan Hajnoczi]

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On Tue, Jan 31, 2017 at 02:23:08PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Current implementation invalidates firstly parent bds and then its
> children. This leads to the following bug:
> 
> after incoming migration, in bdrv_invalidate_cache_all:
> 1. invalidate parent bds - reopen it with BDRV_O_INACTIVE cleared
> 2. child is not yet invalidated
> 3. parent check that its BDRV_O_INACTIVE is cleared
> 4. parent writes to child
> 5. assert in bdrv_co_pwritev, as BDRV_O_INACTIVE is set for child
> 
> This patch fixes it by just changing invalidate sequence: invalidate
> children first.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> v2: I've missed that bdrv_invalidate_cache is already recursive, so we
> can change sequence here. Also v1 doesn't cover the case when
> bdrv_invalidate_cache is called not from bdrv_invalidate_cache_all.
> 
>  block.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [Qemu-devel] [PATCH] block: bdrv_invalidate_cache: invalidate children first

[Max Reitz]

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On 31.01.2017 12:23, Vladimir Sementsov-Ogievskiy wrote:
> Current implementation invalidates firstly parent bds and then its
> children. This leads to the following bug:
> 
> after incoming migration, in bdrv_invalidate_cache_all:
> 1. invalidate parent bds - reopen it with BDRV_O_INACTIVE cleared
> 2. child is not yet invalidated
> 3. parent check that its BDRV_O_INACTIVE is cleared
> 4. parent writes to child
> 5. assert in bdrv_co_pwritev, as BDRV_O_INACTIVE is set for child
> 
> This patch fixes it by just changing invalidate sequence: invalidate
> children first.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> v2: I've missed that bdrv_invalidate_cache is already recursive, so we
> can change sequence here. Also v1 doesn't cover the case when
> bdrv_invalidate_cache is called not from bdrv_invalidate_cache_all.

Thanks, applied to my block tree:

https://github.com/XanClic/qemu/commits/block

Max


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