[PATCH] x86: text_poke might sleep

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* Peter Zijlstra (peterz@infradead.org) wrote:

> 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.
> 
> Anybody got an idea on how to fix this?

Add might_sleep(), comments and use local_irq_disable/enable in text_poke so
people are really aware that it uses vmap, which sleeps.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Ingo Molnar <mingo@elte.hu>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Nick Piggin <npiggin@suse.de>
CC: akpm <akpm@linux-foundation.org>
---
 arch/x86/kernel/alternative.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6-lttng/arch/x86/kernel/alternative.c
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/alternative.c	2009-02-13 09:02:20.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/alternative.c	2009-02-13 09:05:05.000000000 -0500
@@ -494,16 +494,16 @@ void *text_poke_early(void *addr, const 
  * Only atomic text poke/set should be allowed when not doing early patching.
  * It means the size must be writable atomically and the address must be aligned
  * in a way that permits an atomic write. It also makes sure we fit on a single
- * page.
+ * page. Should be called with preemption enabled.
  */
 void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
 {
-	unsigned long flags;
 	char *vaddr;
 	int nr_pages = 2;
 	struct page *pages[2];
 	int i;
 
+	might_sleep();
 	if (!core_kernel_text((unsigned long)addr)) {
 		pages[0] = vmalloc_to_page(addr);
 		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
@@ -517,9 +517,9 @@ void *__kprobes text_poke(void *addr, co
 		nr_pages = 1;
 	vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
 	BUG_ON(!vaddr);
-	local_irq_save(flags);
+	local_irq_disable();
 	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
-	local_irq_restore(flags);
+	local_irq_enable();
 	vunmap(vaddr);
 	sync_core();
 	/* Could also do a CLFLUSH here to speed up CPU recovery; but

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