Re: [Qemu-block] [PATCH v1 1/1] qemu/migration: fix the double free problem on from_src_file

[QingFeng Hao]

在 2017/6/6 11:50, Peter Xu 写道:
> On Tue, Jun 06, 2017 at 11:38:05AM +0800, QingFeng Hao wrote:
> > 在 2017/6/6 11:03, Peter Xu 写道:
> > > On Mon, Jun 05, 2017 at 12:48:51PM +0200, QingFeng Hao wrote:
> > > > In load_vmstate, mis->from_src_file is freed twice, the first free is by
> > > > qemu_fclose, the second is by migration_incoming_state_destroy and
> > > > it causes Illegal instruction exception. The fix is just to remove the
> > > > first free.
> > > >
> > > > This problem is found by qemu-iotests case 068 since commit
> > > > "660819b migration: shut src return path unconditionally". The error is:
> > > > 068 1s ... - output mismatch (see 068.out.bad)
> > > >      --- tests/qemu-iotests/068.out     2017-05-06 01:00:26.417270437 +0200
> > > >      +++ 068.out.bad    2017-06-03 13:59:55.360274640 +0200
> > > >      @@ -6,6 +6,8 @@
> > > >       QEMU X.Y.Z monitor - type 'help' for more information
> > > >       (qemu) savevm 0
> > > >       (qemu) quit
> > > >      +./common.config: line 107: 242472 Illegal instruction     (core dumped) ( if [ -n 
> > > > "${QEMU_NEED_PID}" ]; then
> > > >      +    echo $BASHPID > "${QEMU_TEST_DIR}/qemu-${_QEMU_HANDLE}.pid";
> > > >      +fi; exec "$QEMU_PROG" $QEMU_OPTIONS "$@" )
> > > >       QEMU X.Y.Z monitor - type 'help' for more information
> > > >      -(qemu) quit
> > > >      -*** done
> > > >      +(qemu) *** done
> > > >
> > > > Signed-off-by: QingFeng Hao <address@hidden>
> > > > ---
> > > >   migration/savevm.c | 1 -
> > > >   1 file changed, 1 deletion(-)
> > > >
> > > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > > index 9c320f59d0..853e14e34e 100644
> > > > --- a/migration/savevm.c
> > > > +++ b/migration/savevm.c
> > > > @@ -2290,7 +2290,6 @@ int load_snapshot(const char *name, Error **errp)
> > > >       aio_context_acquire(aio_context);
> > > >       ret = qemu_loadvm_state(f);
> > > > -    qemu_fclose(f);
> > > >       aio_context_release(aio_context);
> > > >       migration_incoming_state_destroy();
> > > Thanks QingFeng for the fix!
> > >
> > > Reviewed-by: Peter Xu <address@hidden>
> > >
> > > Though here instead of removing the fclose(), not sure whether this is
> > > nicer:
> > >
> > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > index 9c320f5..1feb519 100644
> > > --- a/migration/savevm.c
> > > +++ b/migration/savevm.c
> > > @@ -2233,7 +2233,6 @@ int load_snapshot(const char *name, Error **errp)
> > >       QEMUFile *f;
> > >       int ret;
> > >       AioContext *aio_context;
> > > -    MigrationIncomingState *mis = migration_incoming_get_current();
> > >
> > >       if (!bdrv_all_can_snapshot(&bs)) {
> > >           error_setg(errp,
> > > @@ -2286,7 +2285,6 @@ int load_snapshot(const char *name, Error **errp)
> > >       }
> > >
> > >       qemu_system_reset(SHUTDOWN_CAUSE_NONE);
> > > -    mis->from_src_file = f;
> > >
> > >       aio_context_acquire(aio_context);
> > >       ret = qemu_loadvm_state(f);
> > Thanks Peter. I have a doubt on this change because I see there are several
> > places
> > referencing from_src_file e.g. loadvm_postcopy_ram_handle_discard, and it
> > seems to
> > get byte from the file and it's called by qemu_loadvm_state.
> > Anyway, you remind me for the description that is "In load_snapshot" rather
> > than
> > "In load_vmstate". thanks
> Oh I didn't really notice that. :)
>
> It shouldn't affect imho since load snapshot won't trigger postcopy
> codes. But sure current fix is good enough for me at least.
Ok, thanks!
> Thanks,

--
Regards
QingFeng Hao