I noticed this when poking around in this area.
BTW, the comments in oops_begin say the operation is racy, and the only
way I can think of that is races is if you get a non-NMI oops then
get an NMI oops within the oops_begin or oops_end functions.
That can actually be fixed using compare-and-swap, but, to tell you
the truth, it just doesn't seem worth it to me. If you like, though,
I can attempt a fix at that, too. Anyway, the patch...
The oops_begin() function in x86_64 would only conditionally claim
the die_lock if the call is nested, but oops_end() would always
release the spinlock. This patch adds a nest count for the die lock
so that the release of the lock is only done on the final oops_end().
Signed-off-by: Corey Minyard <[email protected]>
diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 6bda322..debd834 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -384,6 +384,7 @@ void out_of_line_bug(void)
static DEFINE_SPINLOCK(die_lock);
static int die_owner = -1;
+static unsigned int die_nest_count;
unsigned __kprobes long oops_begin(void)
{
@@ -398,6 +399,7 @@ unsigned __kprobes long oops_begin(void)
else
spin_lock(&die_lock);
}
+ die_nest_count++;
die_owner = cpu;
console_verbose();
bust_spinlocks(1);
@@ -408,7 +410,13 @@ void __kprobes oops_end(unsigned long fl
{
die_owner = -1;
bust_spinlocks(0);
- spin_unlock_irqrestore(&die_lock, flags);
+ die_nest_count--;
+ if (die_nest_count)
+ /* We still own the lock */
+ local_irq_restore(flags);
+ else
+ /* Nest count reaches zero, release the lock. */
+ spin_unlock_irqrestore(&die_lock, flags);
if (panic_on_oops)
panic("Oops");
}
-
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