On Thu, Apr 06, 2017 at 04:23:19PM -0500, Eric Blake wrote:
> On 04/06/2017 04:15 PM, Richard W.M. Jones wrote:
>
> >>>> +++ b/block/io.c
> >>>> @@ -945,6 +945,8 @@ static int coroutine_fn
> >>>> bdrv_co_do_copy_on_readv(BdrvChild *child,
> >>>> size_t skip_bytes;
> >>>> int ret;
> >>>>
> >>>> + assert(child->perm & (BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE));
> >>>
>
> > https://bugzilla.redhat.com/show_bug.cgi?id=1439922
> >
> > There is also a minimal reproducer in comment 2.
>
> If it helps, backtrace shows:
>
> #4 0x0000555555c09f10 in bdrv_co_do_copy_on_readv
> (child=0x555556990180, offset=0, bytes=512, qiov=0x7fffffffd0c0) at
> block/io.c:948
> #5 0x0000555555c0a33d in bdrv_aligned_preadv (child=0x555556990180,
> req=0x7fffb6dffec0, offset=0, bytes=512, align=1, qiov=0x7fffffffd0c0,
> flags=1)
> at block/io.c:1058
> #6 0x0000555555c0a8c3 in bdrv_co_preadv (child=0x555556990180,
> offset=0, bytes=512, qiov=0x7fffffffd0c0, flags=BDRV_REQ_COPY_ON_READ)
> at block/io.c:1166
> #7 0x0000555555bf7ccf in blk_co_preadv (blk=0x555556a2bc20, offset=0,
> bytes=512, qiov=0x7fffffffd0c0, flags=0) at block/block-backend.c:927
> #8 0x0000555555bf7e19 in blk_read_entry (opaque=0x7fffffffd0e0)
> at block/block-backend.c:974
> #9 0x0000555555cc3015 in coroutine_trampoline (i0=1485566720, i1=21845)
> at util/coroutine-ucontext.c:79
The patch that fixes this is simply:
diff --git a/block/io.c b/block/io.c
index 2709a7007f..4f1a730e45 100644
--- a/block/io.c
+++ b/block/io.c
@@ -945,8 +945,6 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild
*child,
size_t skip_bytes;
int ret;
- assert(child->perm & (BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE));
-
/* Cover entire cluster so no additional backing file I/O is required when
* allocating cluster in the image file.
*/
It has no ill effects that I can see, and fixes the libguestfs test
suite, but I'm assuming the assert was added for a reason so I'm not
proposing this as a patch.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
Fedora Windows cross-compiler. Compile Windows programs, test, and
build Windows installers. Over 100 libraries supported.
http://fedoraproject.org/wiki/MinGW
