[Devel] Re: [PATCH 13/28] [PREP 13/14] Miscellaneous preparations in pid namespaces

[sukadev at us.ibm.com]

Pavel Emelianov [xemul at openvz.org] wrote:
| sukadev at us.ibm.com wrote:
| > Pavel Emelianov [xemul at openvz.org] wrote:
| > | The most important one is moving exit_task_namespaces behind exit_notify
| > | in do_exit() to make it possible to see the task's pid namespace to
| > | properly notify the parent.
| > 
| > Hmm. I think we tried this once a few months ago and got a crash in nfsd
| > See http://lkml.org/lkml/2007/1/17/75
| > 
| >             [<c01f6115>] lockd_down+0x125/0x190
| >             [<c01d26bd>] nfs_free_server+0x6d/0xd0
| >             [<c01d8e9c>] nfs_kill_super+0xc/0x20
| >             [<c0161c5d>] deactivate_super+0x7d/0xa0
| >             [<c0175e0e>] release_mounts+0x6e/0x80
| >             [<c0175e86>] __put_mnt_ns+0x66/0x80
| >             [<c0132b3e>] free_nsproxy+0x5e/0x60
| >                 // exit_task_namespaces() after returning from exit_notify()
| >             [<c011f021>] do_exit+0x791/0x810
| >             [<c011f0c6>] do_group_exit+0x26/0x70
| >             [<c0103142>] sysenter_past_esp+0x5f/0x85
| > 
| > exit_notify() sets current->sighand to NULL and I think lockd_down() called
| > from exit_task_namespaces/__put_mnt_ns() was accesssing current->sighand.
| 
| If sighand is set to NULL and then accessed then how is this related to pid namespace? 

Switching the order of exit_notify() and exit_task_namespaces() is what
caused the problem when we did it before.

If you exit_task_namespaces() before exit_notify() as the mainline code
does, you won't see this bc nfsd would have freed its super by then.

| 
| > Do your other patches in this set tweak something to prevent it ?
| 
| I think no. I'll check it for my current patches.

Buried in that thread was a test case to repro the problem. Maybe that
will help.

| 
| > Thats one of the reasons we had to remove pid_ns from nsproxy and use
| > the pid_ns from pid->upid_list[i]->pid_ns.
| > 
| > Suka
| > 
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