Per-task and per-cpu breakpoints have to be unambiguously identified for
proper restoration of hw-breakpoints. The notion of pure user- and kernel-
space breakpoints is antiquated. Store 'pid' of the process against which
the perf-counter was requested to help proper distinction.
This helps seamless handling of kernel-space breakpoints within the context
of a user-space process and breakpoints for kernel-threads.
Signed-off-by: K.Prasad <pra...@linux.vnet.ibm.com>
---
arch/powerpc/kernel/hw_breakpoint.c | 24 +++++++++++++++++-------
include/linux/perf_event.h | 1 +
kernel/perf_event.c | 9 ++++++---
3 files changed, 24 insertions(+), 10 deletions(-)
Index: linux-2.6.ppc64_test/include/linux/perf_event.h
===================================================================
--- linux-2.6.ppc64_test.orig/include/linux/perf_event.h
+++ linux-2.6.ppc64_test/include/linux/perf_event.h
@@ -698,6 +698,7 @@ struct perf_event {
int oncpu;
int cpu;
+ pid_t pid;
struct list_head owner_entry;
struct task_struct *owner;
Index: linux-2.6.ppc64_test/kernel/perf_event.c
===================================================================
--- linux-2.6.ppc64_test.orig/kernel/perf_event.c
+++ linux-2.6.ppc64_test/kernel/perf_event.c
@@ -4684,6 +4684,7 @@ static const struct pmu *sw_perf_event_i
static struct perf_event *
perf_event_alloc(struct perf_event_attr *attr,
int cpu,
+ pid_t pid,
struct perf_event_context *ctx,
struct perf_event *group_leader,
struct perf_event *parent_event,
@@ -4717,6 +4718,7 @@ perf_event_alloc(struct perf_event_attr
mutex_init(&event->mmap_mutex);
event->cpu = cpu;
+ event->pid = pid;
event->attr = *attr;
event->group_leader = group_leader;
event->pmu = NULL;
@@ -5015,7 +5017,7 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_put_context;
}
- event = perf_event_alloc(&attr, cpu, ctx, group_leader,
+ event = perf_event_alloc(&attr, cpu, pid, ctx, group_leader,
NULL, NULL, GFP_KERNEL);
err = PTR_ERR(event);
if (IS_ERR(event))
@@ -5090,7 +5092,7 @@ perf_event_create_kernel_counter(struct
goto err_exit;
}
- event = perf_event_alloc(attr, cpu, ctx, NULL,
+ event = perf_event_alloc(attr, cpu, pid, ctx, NULL,
NULL, overflow_handler, GFP_KERNEL);
if (IS_ERR(event)) {
err = PTR_ERR(event);
@@ -5142,7 +5144,8 @@ inherit_event(struct perf_event *parent_
parent_event = parent_event->parent;
child_event = perf_event_alloc(&parent_event->attr,
- parent_event->cpu, child_ctx,
+ parent_event->cpu, child->pid,
+ child_ctx,
group_leader, parent_event,
NULL, GFP_KERNEL);
if (IS_ERR(child_event))
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/hw_breakpoint.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
@@ -221,7 +221,7 @@ void thread_change_pc(struct task_struct
*/
int __kprobes hw_breakpoint_handler(struct die_args *args)
{
- bool is_kernel, is_ptrace_bp = false;
+ bool is_kernel, is_taskbound_bp, is_ptrace_bp = false;
int rc = NOTIFY_STOP;
struct perf_event *bp;
struct pt_regs *regs = args->regs;
@@ -246,6 +246,7 @@ int __kprobes hw_breakpoint_handler(stru
is_kernel = is_kernel_addr(bp->attr.bp_addr);
is_ptrace_bp = (bp->overflow_handler == ptrace_triggered) ?
true : false;
+ is_taskbound_bp = (bp->pid > 0) ? true : false;
/*
* Verify if dar lies within the address range occupied by the symbol
@@ -288,7 +289,14 @@ int __kprobes hw_breakpoint_handler(stru
/* emulate_step() could not execute it, single-step them */
if (stepped == 0) {
regs->msr |= MSR_SE;
- __get_cpu_var(last_hit_bp) = bp;
+ /*
+ * Kernel-space addresses can also be bound to a task. If so,
+ * store the breakpoint in its 'thread_struct'
+ */
+ if (is_taskbound_bp)
+ bp->ctx->task->thread.last_hit_ubp = bp;
+ else
+ __get_cpu_var(last_hit_bp) = bp;
goto out;
}
/*
@@ -310,17 +318,17 @@ out:
int __kprobes single_step_dabr_instruction(struct die_args *args)
{
struct pt_regs *regs = args->regs;
- struct perf_event *bp = NULL, *kernel_bp, *user_bp;
+ struct perf_event *bp = NULL, *kernel_bp, *per_task_bp;
struct arch_hw_breakpoint *bp_info;
/*
* Identify the cause of single-stepping and find the corresponding
* breakpoint structure
*/
- user_bp = current->thread.last_hit_ubp;
+ per_task_bp = current->thread.last_hit_ubp;
kernel_bp = __get_cpu_var(last_hit_bp);
- if (user_bp) {
- bp = user_bp;
+ if (per_task_bp) {
+ bp = per_task_bp;
current->thread.last_hit_ubp = NULL;
} else if (kernel_bp) {
bp = kernel_bp;
@@ -348,7 +356,9 @@ int __kprobes single_step_dabr_instructi
* for kernel-space breakpoints, so this cannot work along with other
* debuggers (like KGDB, xmon) which may be single-stepping kernel code.
*/
- if (!(user_bp && test_thread_flag(TIF_SINGLESTEP)))
+ if (!(per_task_bp &&
+ (!is_kernel_addr(bp->attr.bp_addr)) &&
+ test_thread_flag(TIF_SINGLESTEP)))
regs->msr &= ~MSR_SE;
set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
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