[Devel] Re: [PATCH 3/4] proc: simplify remove_proc_entry() wrt locking

[Alexey Dobriyan]

On Tue, Nov 20, 2007 at 08:08:42PM -0800, Andrew Morton wrote:
> On Fri, 16 Nov 2007 18:10:15 +0300 Alexey Dobriyan <adobriyan at sw.ru> wrote:
> 
> > We can take proc_subdir_lock for duration of list searching and removing
> > from lists only. It can't hurt -- we can gather any amount of looked up
> > PDEs right after proc_subdir_lock droppage in proc_lookup() anyway.
> > Current code should already deal with this correctly.
> > 
> > Also this should make code more undestandable:
> > * original looks like a loop, however, it's a loop with unconditional
> >   trailing "break;" -- not loop at all.
> > * more explicit statement that proc_subdir_lock protects only ->subdir lists.
> 
> oopses the Vaio.
> 
> 
> [   12.595145] BUG: unable to handle kernel NULL pointer dereference at virtual address 00000030
> [   12.598487] printing eip: c01a607f *pde = 00000000 
> [   12.601795] Oops: 0000 [#1] PREEMPT 
> [   12.605101] last sysfs file: 
> [   12.608432] Modules linked in:
> [   12.611727] 
> [   12.615000] Pid: 1, comm: swapper Not tainted (2.6.24-rc3-mm1 #4)
> [   12.618345] EIP: 0060:[<c01a607f>] EFLAGS: 00010206 CPU: 0
> [   12.621713] EIP is at remove_proc_entry+0x69/0x16c
> [   12.625071] EAX: 00000000 EBX: f726d940 ECX: f726d9bd EDX: 00000000
> [   12.628445] ESI: 00000030 EDI: f726d940 EBP: f7841e3c ESP: f7841dcc
> [   12.631747]  DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
> [   12.635052] Process swapper (pid: 1, ti=F7840000 task=F783ED30 task.ti=F7840000)
> [   12.635181] Stack: 00000005 f726d9c0 c042747c f7841df0 c0131992 00000282 f7841e1c 00000005 
> [   12.638669]        00000000 00000046 00000174 00000000 c0138012 00000000 00000000 00000000 
> [   12.642173]        f783f2e0 f783ed30 00000000 f783ed30 c0320d27 00000010 f7841e34 c013a1e4 
> [   12.645623] Call Trace:
> [   12.652432]  [<c0104e0c>] show_trace_log_lvl+0x12/0x25
> [   12.655938]  [<c0104eab>] show_stack_log_lvl+0x8c/0x9e
> [   12.659333]  [<c0104f47>] show_registers+0x8a/0x1c0
> [   12.662755]  [<c010516b>] die+0xee/0x1c4
> [   12.666101]  [<c0117a18>] do_page_fault+0x405/0x4e1
> [   12.669427]  [<c0320fda>] error_code+0x6a/0x70
> [   12.672700]  [<c0151d13>] unregister_handler_proc+0x1b/0x1d
> [   12.675974]  [<c0150bb2>] free_irq+0xb3/0xdc
> [   12.679227]  [<c028a51b>] yenta_probe_cb_irq+0xc9/0xd6
> [   12.682482]  [<c028a829>] ti12xx_override+0x12b/0x4c5
> [   12.685782]  [<c028b270>] yenta_probe+0x2b1/0x55d
> [   12.689042]  [<c01fed0d>] pci_device_probe+0x39/0x5b
> [   12.692276]  [<c025a9ad>] driver_probe_device+0xd1/0x147
> [   12.695492]  [<c025ab37>] __driver_attach+0x6a/0xa1
> [   12.698666]  [<c0259ee9>] bus_for_each_dev+0x37/0x5c
> [   12.701783]  [<c025a816>] driver_attach+0x14/0x16
> [   12.704891]  [<c025a220>] bus_add_driver+0x7a/0x191
> [   12.708015]  [<c025ad08>] driver_register+0x57/0x5c
> [   12.711095]  [<c01fee6f>] __pci_register_driver+0x56/0x83
> [   12.714170]  [<c047203c>] yenta_socket_init+0x14/0x16
> [   12.717195]  [<c0458650>] kernel_init+0xc5/0x20f
> [   12.720120]  [<c0104aaf>] kernel_thread_helper+0x7/0x10
> [   12.723041]  =======================
> [   12.725918] INFO: lockdep is turned off.
> [   12.728813] Code: 75 94 83 c6 38 eb 24 8b 55 f0 89 d9 8b 45 90 e8 ab fe ff ff 85 c0 74 0e 8b 43 30 89 df 89 06 c7 43 30 00 00 00 00 8b 36 83 c6 30 <8b> 1e 85 db 75 d6 b8 e0 2b 43 c0 e8 ab ab 17 00 85 ff 0f 84 e3 
> [   12.735473] EIP: [<c01a607f>] remove_proc_entry+0x69/0x16c SS:ESP 0068:f7841dcc
> 
> (gdb) l *0xc01a4fdf
> 0xc01a4fdf is in remove_proc_entry (fs/proc/generic.c:698).
> warning: Source file is more recent than executable.
> 
> 693             if (!parent && xlate_proc_name(name, &parent, &fn) != 0)
> 694                     return;
> 695             len = strlen(fn);
> 696     
> 697             spin_lock(&proc_subdir_lock);
> 698             for (p = &parent->subdir; *p; p=&(*p)->next ) {
> 699                     if (!proc_match(len, fn, *p))
> 700                             continue;
> 701                     de = *p;
> 702                     *p = de->next;
  703			  de->next = NULL;

			  break;	<===

  704		  }
> 
> iirc this is what Andy was hitting.

Doh! this was missing "break;". I'll resend the patch and refcounting fixes
soon.

P.S.: Do you make notches on Vaio-of-death?