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authorFrederic Weisbecker <fweisbec@gmail.com>2009-12-09 09:25:48 +0100
committerIngo Molnar <mingo@elte.hu>2009-12-09 09:48:20 +0100
commit44234adcdce38f83c56e05f808ce656175b4beeb (patch)
treecaff2ca7bbf4bf7c0b12652caf739bcc6db5f4d3 /kernel
parentc937fe20cb6d9e24c6ad5f9f0c64d64c78411057 (diff)
downloadlinux-linaro-44234adcdce38f83c56e05f808ce656175b4beeb.tar.gz
hw-breakpoints: Modify breakpoints without unregistering them
Currently, when ptrace needs to modify a breakpoint, like disabling it, changing its address, type or len, it calls modify_user_hw_breakpoint(). This latter will perform the heavy and racy task of unregistering the old breakpoint and registering a new one. This is racy as someone else might steal the reserved breakpoint slot under us, which is undesired as the breakpoint is only supposed to be modified, sometimes in the middle of a debugging workflow. We don't want our slot to be stolen in the middle. So instead of unregistering/registering the breakpoint, just disable it while we modify its breakpoint fields and re-enable it after if necessary. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Prasad <prasad@linux.vnet.ibm.com> LKML-Reference: <1260347148-5519-1-git-send-regression-fweisbec@gmail.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/hw_breakpoint.c42
-rw-r--r--kernel/perf_event.c4
2 files changed, 34 insertions, 12 deletions
diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
index 03a0773ac2b..366eedf949c 100644
--- a/kernel/hw_breakpoint.c
+++ b/kernel/hw_breakpoint.c
@@ -320,18 +320,40 @@ EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
* @triggered: callback to trigger when we hit the breakpoint
* @tsk: pointer to 'task_struct' of the process to which the address belongs
*/
-struct perf_event *
-modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
+int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
- /*
- * FIXME: do it without unregistering
- * - We don't want to lose our slot
- * - If the new bp is incorrect, don't lose the older one
- */
- unregister_hw_breakpoint(bp);
+ u64 old_addr = bp->attr.bp_addr;
+ int old_type = bp->attr.bp_type;
+ int old_len = bp->attr.bp_len;
+ int err = 0;
+
+ perf_event_disable(bp);
+
+ bp->attr.bp_addr = attr->bp_addr;
+ bp->attr.bp_type = attr->bp_type;
+ bp->attr.bp_len = attr->bp_len;
+
+ if (attr->disabled)
+ goto end;
- return perf_event_create_kernel_counter(attr, -1, bp->ctx->task->pid,
- bp->overflow_handler);
+ err = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
+ if (!err)
+ perf_event_enable(bp);
+
+ if (err) {
+ bp->attr.bp_addr = old_addr;
+ bp->attr.bp_type = old_type;
+ bp->attr.bp_len = old_len;
+ if (!bp->attr.disabled)
+ perf_event_enable(bp);
+
+ return err;
+ }
+
+end:
+ bp->attr.disabled = attr->disabled;
+
+ return 0;
}
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index fd43ff4ac86..3b0cf86eee8 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -567,7 +567,7 @@ static void __perf_event_disable(void *info)
* is the current context on this CPU and preemption is disabled,
* hence we can't get into perf_event_task_sched_out for this context.
*/
-static void perf_event_disable(struct perf_event *event)
+void perf_event_disable(struct perf_event *event)
{
struct perf_event_context *ctx = event->ctx;
struct task_struct *task = ctx->task;
@@ -971,7 +971,7 @@ static void __perf_event_enable(void *info)
* perf_event_for_each_child or perf_event_for_each as described
* for perf_event_disable.
*/
-static void perf_event_enable(struct perf_event *event)
+void perf_event_enable(struct perf_event *event)
{
struct perf_event_context *ctx = event->ctx;
struct task_struct *task = ctx->task;