x86: fix "BUG: sleeping function called from invalid context" in print_vma_addr()

Jiri Kosina reported the following deadlock scenario with
show_unhandled_signals enabled:

 [   68.379022] gnome-settings-[2941] trap int3 ip:3d2c840f34
 sp:7fff36f5d100 error:0<3>BUG: sleeping function called from invalid
 context at kernel/rwsem.c:21
 [   68.379039] in_atomic():1, irqs_disabled():0
 [   68.379044] no locks held by gnome-settings-/2941.
 [   68.379050] Pid: 2941, comm: gnome-settings- Not tainted 2.6.25-rc1 #30
 [   68.379054]
 [   68.379056] Call Trace:
 [   68.379061]  <#DB>  [<ffffffff81064883>] ? __debug_show_held_locks+0x13/0x30
 [   68.379109]  [<ffffffff81036765>] __might_sleep+0xe5/0x110
 [   68.379123]  [<ffffffff812f2240>] down_read+0x20/0x70
 [   68.379137]  [<ffffffff8109cdca>] print_vma_addr+0x3a/0x110
 [   68.379152]  [<ffffffff8100f435>] do_trap+0xf5/0x170
 [   68.379168]  [<ffffffff8100f52b>] do_int3+0x7b/0xe0
 [   68.379180]  [<ffffffff812f4a6f>] int3+0x9f/0xd0
 [   68.379203]  <<EOE>>
 [   68.379229]  in libglib-2.0.so.0.1505.0[3d2c800000+dc000]

and tracked it down to:

  commit 03252919b79891063cf99145612360efbdf9500b
  Author: Andi Kleen <ak@suse.de>
  Date:   Wed Jan 30 13:33:18 2008 +0100

      x86: print which shared library/executable faulted in segfault etc. messages

the problem is that we call down_read() from an atomic context.

Solve this by returning from print_vma_addr() if the preempt count is
elevated. Update preempt_conditional_sti / preempt_conditional_cli to
unconditionally lift the preempt count even on !CONFIG_PREEMPT.

Reported-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/kernel/traps_64.c b/arch/x86/kernel/traps_64.c
index efc66df728b6..045466681911 100644
--- a/arch/x86/kernel/traps_64.c
+++ b/arch/x86/kernel/traps_64.c
@@ -84,7 +84,7 @@ static inline void conditional_sti(struct pt_regs *regs)
 
 static inline void preempt_conditional_sti(struct pt_regs *regs)
 {
-        preempt_disable();
+        inc_preempt_count();
         if (regs->flags & X86_EFLAGS_IF)
                 local_irq_enable();
 }
@@ -95,7 +95,7 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
                 local_irq_disable();
         /* Make sure to not schedule here because we could be running
            on an exception stack. */
-        preempt_enable_no_resched();
+        dec_preempt_count();
 }
 
 int kstack_depth_to_print = 12;