Re: bcache: fix oops bug in cache_set_flush

Hi Coly:
  In addition, the following actions caused the kernel oops. After
creating the BCache device, the metadata information was not cleared.
Hot-plugged to another server, repartitioned nvme with a different
partition size to recreate the BCache device.After the partition was
executed, the kernel oops was triggered.
  After I applied the new patch, it did not trigger the kernel panic.
  For the above problems, can you give me better modification suggestions?
  Thanks!
  cheliequan

liequan che <[email protected]> 于2024年11月13日周三 15:40写道：
>
> I tested this bug on kernel versions 5.10.0-231.0.0.133 and 5.10.0-202.0.0.115。
> You can get detailed information through the link below.
>
> https://gitee.com/openeuler/kernel/issues/IB3YQZ
> https://gitee.com/openeuler/kernel/pulls/13205
> Best Regards！
> cheleiquan
>
> Coly Li <[email protected]> 于2024年11月13日周三 15:04写道：
> >
> > Hi Liequan,
> >
> > > 2024年11月13日 14:25，liequan che <[email protected]> 写道：
> > >
> > > Signed-off-by: cheliequan <[email protected]>
> > >
> > >   If the bcache cache disk contains damaged btree data,
> > > when the bcache cache disk partition is directly operated,
> > > the system-udevd service is triggered to call the bcache-register
> > > program to register the bcache device,resulting in kernel oops.
> > >
> >
> > What is the kernel version ?
> >
> > Interesting that why the btree node checking code during registration doesn’t cache the meta data error.
> >
> >
> >
> > > crash> bt
> > > PID: 7773     TASK: ffff49cc44d69340  CPU: 57   COMMAND: "kworker/57:2"
> > > #0 [ffff800046373800] machine_kexec at ffffbe5039eb54a8
> > > #1 [ffff8000463739b0] __crash_kexec at ffffbe503a052824
> > > #2 [ffff8000463739e0] crash_kexec at ffffbe503a0529cc
> > > #3 [ffff800046373a60] die at ffffbe5039e9445c
> > > #4 [ffff800046373ac0] die_kernel_fault at ffffbe5039ec698c
> > > #5 [ffff800046373af0] __do_kernel_fault at ffffbe5039ec6a38
> > > #6 [ffff800046373b20] do_page_fault at ffffbe503ac76ba4
> > > #7 [ffff800046373b70] do_translation_fault at ffffbe503ac76ebc
> > > #8 [ffff800046373b90] do_mem_abort at ffffbe5039ec68ac
> > > #9 [ffff800046373bc0] el1_abort at ffffbe503ac669bc
> > > #10 [ffff800046373bf0] el1_sync_handler at ffffbe503ac671d4
> > > #11 [ffff800046373d30] el1_sync at ffffbe5039e82230
> > > #12 [ffff800046373d50] cache_set_flush at ffffbe50121fa4c4 [bcache]
> > > #13 [ffff800046373da0] process_one_work at ffffbe5039f5af68
> > > #14 [ffff800046373e00] worker_thread at ffffbe5039f5b3c4
> > > #15 [ffff800046373e50] kthread at ffffbe5039f634b8
> > > crash> dis cache_set_flush+0x94
> > > 0xffffbe50121fa4c8 <cache_set_flush+148>:       str     x23, [x20, #512]
> > >
> > > ---
> > > drivers/md/bcache/super.c | 16 ++++++++++------
> > > 1 file changed, 10 insertions(+), 6 deletions(-)
> > > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> > > index fd97730479d8..8a41dfcf9fb6 100644
> > > --- a/drivers/md/bcache/super.c
> > > +++ b/drivers/md/bcache/super.c
> > > @@ -1741,8 +1741,10 @@ static void cache_set_flush(struct closure *cl)
> > >       if (!IS_ERR_OR_NULL(c->gc_thread))
> > >               kthread_stop(c->gc_thread);
> > >
> > > -       if (!IS_ERR(c->root))
> > > -               list_add(&c->root->list, &c->btree_cache);
> > > +       if (!IS_ERR_OR_NULL(c->root)) {
> > > +               if (!list_empty(&c->root->list))
> > > +                       list_add(&c->root->list, &c->btree_cache);
> > > +       }
> > >
> > >       /*
> > >        * Avoid flushing cached nodes if cache set is retiring
> > > @@ -1750,10 +1752,12 @@ static void cache_set_flush(struct closure *cl)
> > >        */
> > >       if (!test_bit(CACHE_SET_IO_DISABLE, &c->flags))
> > >               list_for_each_entry(b, &c->btree_cache, list) {
> > > -                       mutex_lock(&b->write_lock);
> > > -                       if (btree_node_dirty(b))
> > > -                               __bch_btree_node_write(b, NULL);
> > > -                       mutex_unlock(&b->write_lock);
> > > +                       if (!IS_ERR_OR_NULL(b)) {
> >
> > The above check is not safe.
> >
> >
> >
> > > +                               mutex_lock(&b->write_lock);
> > > +                               if (btree_node_dirty(b))
> > > +                                       __bch_btree_node_write(b, NULL);
> > > +                               mutex_unlock(&b->write_lock);
> > > +                       }
> > >               }
> > >
> > >       if (ca->alloc_thread)
> > > --
> > > 2.33.0
> >
> >
> > Thanks.
> >
> > Coly Li