Re: irq-disabled vs vmap vs text_poke

[Mathieu Desnoyers]

* Masami Hiramatsu (mhiramat@xxxxxxxxxx) wrote:
> Mathieu Desnoyers wrote:
> > * Peter Zijlstra (peterz@xxxxxxxxxxxxx) wrote:
> >> Hi,
> >>
> >> Ingo got the following splat:
> >>
> >> [    5.101748] ------------[ cut here ]------------
> >> [    5.104305] WARNING: at kernel/smp.c:329 smp_call_function_many+0x34/0x1ea()
> >> [    5.104305] Hardware name: P4DC6
> >> [    5.104305] Modules linked in:
> >> [    5.104305] Pid: 1, comm: swapper Not tainted 2.6.29-rc4-tip-01766-g1757c19-dirty #2
> >> [    5.104305] Call Trace:
> >> [    5.104305]  [<c012b5d6>] warn_slowpath+0x79/0x8f
> >> [    5.104305]  [<c0104d24>] ? dump_trace+0x7d/0xac
> >> [    5.104305]  [<c014805a>] ? __lock_acquire+0x319/0x382
> >> [    5.104305]  [<c014d6a1>] smp_call_function_many+0x34/0x1ea
> >> [    5.104305]  [<c011b59e>] ? do_flush_tlb_all+0x0/0x48
> >> [    5.104305]  [<c011b59e>] ? do_flush_tlb_all+0x0/0x48
> >> [    5.104305]  [<c014d878>] smp_call_function+0x21/0x28
> >> [    5.104305]  [<c012fa56>] on_each_cpu+0x14/0x23
> >> [    5.104305]  [<c011b56d>] flush_tlb_all+0x19/0x1b
> >> [    5.104305]  [<c018dcbe>] flush_tlb_kernel_range+0xd/0xf
> >> [    5.104305]  [<c018dd00>] vmap_debug_free_range+0x1c/0x20
> >> [    5.104305]  [<c018e386>] remove_vm_area+0x28/0x67
> >> [    5.104305]  [<c018e468>] __vunmap+0x30/0xab
> >> [    5.104305]  [<c018e50a>] vunmap+0x27/0x29
> >> [    5.104305]  [<c06421b6>] text_poke+0xd6/0x104
> >> [    5.104305]  [<c015687c>] ? kprobe_target+0x0/0x15
> >> [    5.104305]  [<c0642a82>] arch_disarm_kprobe+0x13/0x15
> >> [    5.104305]  [<c06434f9>] __unregister_kprobe_top+0x68/0xe8
> >> [    5.104305]  [<c06436d2>] unregister_kretprobes+0x2c/0xb9
> >> [    5.104305]  [<c0643775>] unregister_kretprobe+0x16/0x18
> >> [    5.104305]  [<c0156d0b>] init_test_probes+0x2ed/0x40c
> >> [    5.104305]  [<c09d451c>] init_kprobes+0x127/0x131
> >> [    5.104305]  [<c01476bf>] ? lock_release_holdtime+0x43/0x48
> >> [    5.104305]  [<c0192e48>] ? __slab_alloc+0x5d/0x27a
> >> [    5.104305]  [<c0147a2a>] ? lockdep_init_map+0x80/0xe7
> >> [    5.104305]  [<c0141c0d>] ? clocksource_read+0xd/0xf
> >> [    5.104305]  [<c0142542>] ? getnstimeofday+0x5e/0xe9
> >> [    5.104305]  [<c013e01e>] ? timespec_to_ktime+0xe/0x11
> >> [    5.104305]  [<c09d43f5>] ? init_kprobes+0x0/0x131
> >> [    5.104305]  [<c010115c>] do_one_initcall+0x6a/0x169
> >> [    5.104305]  [<c029ad2f>] ? number+0x10d/0x1cf
> >> [    5.104305]  [<c0147799>] ? register_lock_class+0x17/0x228
> >> [    5.104305]  [<c014805a>] ? __lock_acquire+0x319/0x382
> >> [    5.104305]  [<c029fa91>] ? debug_check_no_obj_freed+0xda/0x126
> >> [    5.104305]  [<c014805a>] ? __lock_acquire+0x319/0x382
> >> [    5.104305]  [<c01476bf>] ? lock_release_holdtime+0x43/0x48
> >> [    5.104305]  [<c0640ec0>] ? _spin_unlock+0x22/0x25
> >> [    5.104305]  [<c01cc0f0>] ? proc_register+0x14b/0x15c
> >> [    5.104305]  [<c01cc20f>] ? create_proc_entry+0x76/0x8c
> >> [    5.104305]  [<c0162900>] ? default_affinity_write+0x3f/0x8a
> >> [    5.104305]  [<c0162a6a>] ? init_irq_proc+0x58/0x65
> >> [    5.104305]  [<c09bf52d>] kernel_init+0x118/0x169
> >> [    5.104305]  [<c09bf415>] ? kernel_init+0x0/0x169
> >> [    5.104305]  [<c0103adf>] kernel_thread_helper+0x7/0x10
> >> [    5.104305] ---[ end trace e93713a9d40cd06c ]---
> >>
> >> Which points to vunmap() being called with interrupts disabled.
> >>
> >> Which made me look at the vmap/vunmap calls, and they appear to not be
> >> irq-safe, therefore this would be a bug in text_poke().
> >>
> >> [ that is, vmap() can end up calling get_vm_area_caller() which in turn
> >>   calls __get_vm_area_node() with GFP_KERNEL, ergo, don't do this from
> >>   an atomic context. ]
> >>
> >> Now text_poke() uses local_irq_save/restore(), which conveys that it can
> >> be called with IRQs disabled, which is exactly what happens in the trace
> >> above, however we just established that vmap/vunmap() are not irq-safe.
> >>
> > 
> > text_poke should actually use local_irq_disable/enable rather than
> > local_irq_save/restore because it _must_ be called with interrupts on.
> 
> Could you tell me why it must be called with irq on?
> 

Because it uses vmap, but see below..

> > 
> >> Anybody got an idea on how to fix this?
> > 
> > There is probably something wrong with the caller, kprobes, which calls
> > text_poke with interrupts off.
> 
> Hmm, kprobe's smoke test caused this problem. Since (un)register_kprobe()
> may sleep for waiting a mutex, it should not be called with interrupts off.
> So, it's not text_poke()'s issue nor vmap().
> 
> BTW, what about using map_vm_area() in text_poke() instead of vmap()?
> Since text_poke() just maps text pages to alias pages temporarily,
> I think we don't need to use delayed vunmap().
> 

As with this patch from you ? Sorry, when it has been initially
submitted, the discussion turned in a different direction. Please see
comments inline.

> From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> 
> Use vm_map_ram() instead of vmap() in text_poke(), because text_poke()
> just want to map pages temporarily.
> 
> ---
> As far as I tested, this patch works fine for me.
> However, there might be another hidden bug in the kernel...
> We need to fix that too.
> 
>  arch/x86/kernel/alternative.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: 2.6-rc/arch/x86/kernel/alternative.c
> ===================================================================
> --- 2.6-rc.orig/arch/x86/kernel/alternative.c
> +++ 2.6-rc/arch/x86/kernel/alternative.c
> @@ -515,12 +515,12 @@ void *__kprobes text_poke(void *addr, co
>  	BUG_ON(!pages[0]);
>  	if (!pages[1])
>  		nr_pages = 1;
> -	vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
> +	vaddr = vm_map_ram(pages, nr_pages, -1, PAGE_KERNEL);

Hrm, maybe we should do :

  vaddr = vm_map_ram(pages, nr_pages, numa_node_id(), PAGE_KERNEL);

instead ?

Related question : can vm_map_ram sleep ?

Mathieu


>  	BUG_ON(!vaddr);
>  	local_irq_save(flags);
>  	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
>  	local_irq_restore(flags);
> -	vunmap(vaddr);
> +	vm_unmap_ram(vaddr, nr_pages);
>  	sync_core();
>  	/* Could also do a CLFLUSH here to speed up CPU recovery; but
>  	   that causes hangs on some VIA CPUs. */

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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