Re: [PATCH v2] migration/colo: Fix bdrv_graph_rdlock_main_loop: Assertion `!qemu_in_coroutine()' failed.

[Philippe Mathieu-Daudé]

On 17/4/24 08:47, Zhang, Chen wrote:
> > -----Original Message-----
> > From: Philippe Mathieu-Daudé <philmd@linaro.org>
> > Sent: Wednesday, April 17, 2024 2:14 PM
> > To: Li Zhijian <lizhijian@fujitsu.com>; Zhang, Hailiang
> > <zhanghailiang@xfusion.com>; peterx@redhat.com; farosas@suse.de
> > Cc: qemu-devel@nongnu.org; Zhang, Chen <chen.zhang@intel.com>; Wen
> > Congyang <wencongyang2@huawei.com>; Xie Changlong
> > <xiechanglong.d@gmail.com>
> > Subject: Re: [PATCH v2] migration/colo: Fix bdrv_graph_rdlock_main_loop:
> > Assertion `!qemu_in_coroutine()' failed.
> >
> > On 17/4/24 04:56, Li Zhijian via wrote:
> > > bdrv_activate_all() should not be called from the coroutine context,
> > > move it to the QEMU thread colo_process_incoming_thread() with the
> > > bql_lock protected.
> > >
> > > The backtrace is as follows:
> > >    #4  0x0000561af7948362 in bdrv_graph_rdlock_main_loop ()
> > at ../block/graph-lock.c:260
> > >    #5  0x0000561af7907a68 in graph_lockable_auto_lock_mainloop
> > (x=0x7fd29810be7b) at /patch/to/qemu/include/block/graph-lock.h:259
> > >    #6  0x0000561af79167d1 in bdrv_activate_all (errp=0x7fd29810bed0)
> > at ../block.c:6906
> > >    #7  0x0000561af762b4af in colo_incoming_co () at ../migration/colo.c:935
> > >    #8  0x0000561af7607e57 in process_incoming_migration_co (opaque=0x0)
> > at ../migration/migration.c:793
> > >    #9  0x0000561af7adbeeb in coroutine_trampoline (i0=-106876144,
> > i1=22042) at ../util/coroutine-ucontext.c:175
> > >    #10 0x00007fd2a5cf21c0 in  () at /lib64/libc.so.6
> > >
> > > CC: Fabiano Rosas <farosas@suse.de>
> >
> > Cc: qemu-stable@nongnu.org
> >
> > > Closes: https://gitlab.com/qemu-project/qemu/-/issues/2277
> > > Fixes: 2b3912f135 ("block: Mark bdrv_first_blk() and
> > > bdrv_is_root_node() GRAPH_RDLOCK")
> > > Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
>
> It looks good to me. And already verified this patch in my environment.
> After address Phillippe's comments

(I'm only suggesting, in case using the macro results in code
more easily maintainable)

> please add:
>
> Reviewed-by: Zhang Chen <chen.zhang@intel.com>
> Tested-by: Zhang Chen <chen.zhang@intel.com>
>
> Thanks
> Chen
>
> > > ---
> > > V2: fix missing bql_unlock() in error path.
> > > ---
> > >    migration/colo.c | 18 ++++++++++--------
> > >    1 file changed, 10 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/migration/colo.c b/migration/colo.c index
> > > 84632a603e..5600a43d78 100644
> > > --- a/migration/colo.c
> > > +++ b/migration/colo.c
> > > @@ -835,6 +835,16 @@ static void *colo_process_incoming_thread(void
> > *opaque)
> > >            return NULL;
> > >        }
> > >
> > > +    /* Make sure all file formats throw away their mutable metadata */
> > > +    bql_lock();
> >
> > Note there is also the convenient BQL_LOCK_GUARD() macro.
> >
> > > +    bdrv_activate_all(&local_err);
> > > +    if (local_err) {
> > > +        bql_unlock();
> > > +        error_report_err(local_err);
> > > +        return NULL;
> > > +    }
> > > +    bql_unlock();
> > > +
> > >        failover_init_state();