[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, 12 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 27b0c40601fb..cfab48566db1 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -179,6 +179,18 @@ static inline int kprobe_handler(struct pt_regs *regs)
                         kcb->kprobe_status = KPROBE_REENTER;
                         return 1;
                 } else {
+                        if (*addr != BREAKPOINT_INSTRUCTION) {
+                                /* If trap variant, then it belongs not to us */
+                                kprobe_opcode_t cur_insn = *addr;
+                                if (is_trap(cur_insn))
+                                        goto no_kprobe;
+                                /* 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;
+                        }
                         p = __get_cpu_var(current_kprobe);
                         if (p->break_handler && p->break_handler(p, regs)) {
                                 goto ss_probe;