Messages in this thread | | | From | Nikolay Borisov <> | Date | Fri, 23 Sep 2016 16:35:04 +0300 | Subject | Re: BUG_ON in rcu_sync_func triggered |
| |
On Wed, Sep 14, 2016 at 3:58 PM, Oleg Nesterov <oleg@redhat.com> wrote: > On 09/14, Nikolay Borisov wrote: >> >> [ 557.006656] [<ffffffff81307a9b>] dump_stack+0x6b/0xa0 >> [ 557.012737] [<ffffffff81054a85>] warn_slowpath_common+0x95/0xe0 >> [ 557.019781] [<ffffffff81054aea>] warn_slowpath_null+0x1a/0x20 >> [ 557.026645] [<ffffffff810ab9a8>] rcu_sync_enter+0x148/0x1a0 >> [ 557.033309] [<ffffffff8109c9be>] percpu_down_write+0x1e/0xf0 >> [ 557.040074] [<ffffffff81315683>] ? call_rwsem_down_write_failed+0x13/0x20 >> [ 557.048092] [<ffffffff811a868b>] freeze_super+0xab/0x1b0 >> [ 557.054456] [<ffffffff811b7c0d>] do_vfs_ioctl+0x29d/0x560 >> [ 557.060920] [<ffffffff811aae7e>] ? SYSC_newfstat+0x2e/0x40 >> [ 557.067480] [<ffffffff811b7f62>] SyS_ioctl+0x92/0xa0 >> [ 557.073465] [<ffffffff8163c357>] entry_SYSCALL_64_fastpath+0x12/0x6a >> [ 557.081015] ---[ end trace fc087420ac1d8f16 ]--- >> [ 557.086507] XXX: ffff880473326b08 gp=2 cnt=-1 cb=1 >> [ 557.092326] rbd: rbd19: added with size 0x500000000 >> >> This is: if (WARN_ON(rsp->gp_count < 0)) xxx(rsp); > > Thanks a lot. This is what I wanted to see. However, I can't understand why > you did not hit the similar WARN_ON(rsp->gp_count <= 0) in rcu_sync_exit() > before that. > > OK, in any case this doesn't look as a bug in rcu/sync.c, could you please > try the fix below? Not sure it will help, perhaps there is something else... > No need to revert the previous debugging patch. > > Thanks, > > Oleg. > > > diff --git a/fs/super.c b/fs/super.c > index d78b984..a90bdff 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -1344,7 +1344,9 @@ int thaw_super(struct super_block *sb) > int error; > > down_write(&sb->s_umount); > - if (sb->s_writers.frozen == SB_UNFROZEN) { > + if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) { > + if (sb->s_writers.frozen != SB_UNFROZEN) > + pr_crit("THAW: hit the race: %d\n", sb->s_writers.frozen); > up_write(&sb->s_umount); > return -EINVAL; > } >
I was away on holiday so that's why I was silent. However, with this patch applied I couldn't reproduce the issue nor the pr_crit triggered. Have you had any moments of epiphany re. this issue? Should some FS people be involved in the discussion?
| |