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Message-ID: <20090213165555.GA4684@Krystal> Date: Fri, 13 Feb 2009 11:55:55 -0500 From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> To: Masami Hiramatsu <mhiramat@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, Nick Piggin <npiggin@...e.de>, akpm <akpm@...ux-foundation.org>, linux-kernel <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: irq-disabled vs vmap vs text_poke * Masami Hiramatsu (mhiramat@...hat.com) wrote: > Mathieu Desnoyers wrote: > > * Peter Zijlstra (peterz@...radead.org) 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@...hat.com> > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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