[PATCH] kprobes: fix race in recovery of reentrant probe

There is a window where a probe gets removed right after the probe is hit
on some different cpu.  In this case probe handlers can't find a matching
probe instance related to break address.  In this case we need to read the
original instruction at break address to see if that is not a break/int3
instruction and recover safely.

Previous code had a bug where we were not checking for the above race in
case of reentrant probes and the below patch fixes this race.

Tested on IA64, Powerpc, x86_64.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index 4de7f6759093..346fedf9ea47 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -638,6 +638,13 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
                         if (p->break_handler && p->break_handler(p, regs)) {
                                 goto ss_probe;
                         }
+                } else if (!is_ia64_break_inst(regs)) {
+                        /* The breakpoint instruction was removed by
+                         * another cpu right after we hit, no further
+                         * handling of this interrupt is appropriate
+                         */
+                        ret = 1;
+                        goto no_kprobe;
                 } else {
                         /* Not our break */
                         goto no_kprobe;