From: Jan Glauber <jglauber@redhat.com> Subject: [RHEL5.1 PATCH] kprobes breaks BUG_ON on s390 Date: Wed, 07 Mar 2007 13:57:05 +0100 Bugzilla: 231155 Message-Id: <1173272225.5242.31.camel@localhost.localdomain> Changelog: [s390] kprobes breaks BUG_ON BUG_ON is not working correctly on s390. Due to the kprobes notifier only the printk but not the following Oops output is shown if we hit a BUG_ON. The presence of this bug in the GA version of RHEL5 makes me not feel very comfortable, we should fix this early in the 5.1 cycle. More details: The illegal operation handler calls the die notifier with DIE_BPT to let kprobes pick up its breakpoint. If kprobes does not find its breakpoint it returns NOTIFY_STOP instead of NOTIFY_DONE. Since we use stop_machine_run on s390 to arm/disarm the kprobes breakpoints the race that kprobe_handler tries to solve by checking for the kprobes breakpoints does not exist. Removing the check makes BUG_ON working again. Jan jglauber@redhat.com jang@de.ibm.com --- Index: linux-rhel5/arch/s390/kernel/kprobes.c =================================================================== --- linux-rhel5.orig/arch/s390/kernel/kprobes.c 2007-03-05 18:23:29.000000000 +0100 +++ linux-rhel5/arch/s390/kernel/kprobes.c 2007-03-06 14:29:12.000000000 +0100 @@ -343,21 +343,14 @@ static int __kprobes kprobe_handler(stru } p = get_kprobe(addr); - if (!p) { - 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. - * - */ - ret = 1; - } - /* Not one of ours: let kernel handle it */ + if (!p) + /* + * No kprobe at this address. The fault has not been + * caused by a kprobe breakpoint. The race of breakpoint + * vs. kprobe remove does not exist because on s390 we + * use stop_machine_run to arm/disarm the breakpoints. + */ goto no_kprobe; - } kcb->kprobe_status = KPROBE_HIT_ACTIVE; set_current_kprobe(p, regs, kcb);