> My x86_64 system boots fine but crashes as below, when I run my
> 'pidns_exec' test with a simple program that prints getpid(), getppid()
> etc of the process in the child pid ns.
> 
> Pls see 
> 
> http://www.geocities.com/sukadevb/Pidspace/2.6.22-rc6-mm1-pavel-1.tgz
> 
> for the patches I currently have applied and let me know if I need more
> on top.
> 
> And see
> 
> http://www.geocities.com/sukadevb/Pidspace/Test1/
> 
> for the test programs. You may need to run the 'mypid-loop.x' script
> to repro the crash. The pidns_exec.c program calls clone() with CLONE_NEWPID
> and execs the given program (it was included in Patch 0 of the patchset I
> posted to Containers).
> 
> Suka
> 
> login: Unable to handle kernel NULL pointer dereference at 00000000000002fc RIP:
>  [<ffffffff802b9e5e>] proc_get_sb+0xfb/0x138
> PGD 104d53067 PUD 104d4d067 PMD 0
> Oops: 0002 [1] SMP
> CPU 2
> Modules linked in:
> Pid: 3279, comm: pidns_exec Not tainted 2.6.22-rc6-mm1-ovz1 #10
> RIP: 0010:[<ffffffff802b9e5e>]  [<ffffffff802b9e5e>] proc_get_sb+0xfb/0x138
> RSP: 0018:ffff8101029d7d28  EFLAGS: 00010202
> RAX: ffff810100651840 RBX: ffff810104461400 RCX: ffff810100651878
> RDX: 0000000000000000 RSI: ffffffff806e5460 RDI: 0000000000000238
> RBP: ffff810102d886f8 R08: ffff810104461400 R09: ffff810100026000
> R10: 0000000000000000 R11: 0000000000000002 R12: ffff8101029c6000
> R13: 0000000002000000 R14: ffffffff806ee920 R15: ffff810102088cc0
> FS:  00002b0b499ec6f0(0000) GS:ffff81010069c3c0(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 00000000000002fc CR3: 000000010381b000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process pidns_exec (pid: 3279, threadinfo ffff8101029d6000, task ffff81010269e7f0)
> Stack:  ffff810102088cc0 ffff810102088cc0 00000000fffffff4 ffffffff806ee920
>  ffffffff8065f9d9 ffff8101029c6000 0000000002000000 ffffffff80287164
>  00000000000000d0 ffff8101029c6000 ffffffff806e5460 ffff8101029c6000
> Call Trace:
>  [<ffffffff80287164>] vfs_kern_mount+0x4f/0x8b
>  [<ffffffff802b9cf4>] pid_ns_prepare_proc+0x13/0x2e
>  [<ffffffff80245be3>] copy_pid_ns+0xd7/0x164
>  [<ffffffff8024af34>] create_new_namespaces+0xde/0x192
>  [<ffffffff8024b0aa>] copy_namespaces+0x4b/0x85
>  [<ffffffff802347e2>] copy_process+0xcb4/0x1439
>  [<ffffffff8020bbee>] system_call+0x7e/0x83
>  [<ffffffff8023556a>] do_fork+0x6c/0x1e7
>  [<ffffffff8020bf07>] ptregscall_common+0x67/0xb0
> 

Here's the patch fixing the problem. So, Suka, I propose that you review
my patches, point out things that you don't like and would like to see
your code instead. After all I will re-split the set with your fixes, mark
some patches with your From: and send them to Andrew. What do you think?

---

--- ./fs/proc/root.c.procpidnsfix	2007-07-16 10:32:00.000000000 +0400
+++ ./fs/proc/root.c	2007-07-16 12:34:35.000000000 +0400
@@ -79,8 +79,6 @@ static int proc_get_sb(struct file_syste
 		if (!ei->pid)
 			ei->pid = find_get_pid(1);
 		sb->s_flags |= MS_ACTIVE;
-
-		mntput(ns->proc_mnt);
 		ns->proc_mnt = mnt;
 	}
 
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