kprobes/x86: Fix removed int3 checking order

Fix kprobe/x86 to check removed int3 when failing to get kprobe
from hlist. Since we have a time window between checking int3
exists on probed address and getting kprobe on that address,
we can have following scenario:

 -------
 CPU1                     CPU2
 hit int3
 check int3 exists
                          remove int3
                          remove kprobe from hlist
 get kprobe from hlist
 no kprobe->OOPS!
 -------

This patch moves int3 checking if there is no kprobe on that
address for fixing this problem as follows:

 ------
 CPU1                     CPU2
 hit int3
                          remove int3
                          remove kprobe from hlist
 get kprobe from hlist
 no kprobe->check int3 exists
          ->rollback&retry
 ------

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100427223348.2322.9112.stgit@localhost6.localdomain6>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index b43bbae..1658efd 100644 (file)
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -534,20 +534,6 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
        struct kprobe_ctlblk *kcb;
 
        addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
-       if (*addr != BREAKPOINT_INSTRUCTION) {
-               /*
-                * The breakpoint instruction was removed right
-                * after we hit it.  Another cpu has removed
-                * either a probepoint or a debugger breakpoint
-                * at this address.  In either case, no further
-                * handling of this interrupt is appropriate.
-                * Back up over the (now missing) int3 and run
-                * the original instruction.
-                */
-               regs->ip = (unsigned long)addr;
-               return 1;
-       }
-
        /*
         * We don't want to be preempted for the entire
         * duration of kprobe processing. We conditionally
@@ -579,6 +565,19 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                                setup_singlestep(p, regs, kcb, 0);
                        return 1;
                }
+       } else if (*addr != BREAKPOINT_INSTRUCTION) {
+               /*
+                * The breakpoint instruction was removed right
+                * after we hit it.  Another cpu has removed
+                * either a probepoint or a debugger breakpoint
+                * at this address.  In either case, no further
+                * handling of this interrupt is appropriate.
+                * Back up over the (now missing) int3 and run
+                * the original instruction.
+                */
+               regs->ip = (unsigned long)addr;
+               preempt_enable_no_resched();
+               return 1;
        } else if (kprobe_running()) {
                p = __get_cpu_var(current_kprobe);
                if (p->break_handler && p->break_handler(p, regs)) {