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Subject[PATCH 3/6] hw_breakpoint: Add modify_bp_slot function
Date
Adding modify_bp_slot function to keep slot numbers
correct when changing the breakpoint type.

Using existing __release_bp_slot/__reserve_bp_slot
call sequence to update the slot counts.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
kernel/events/hw_breakpoint.c | 46 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 39 insertions(+), 7 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 9b31fbcc3305..776948beb4ac 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -44,6 +44,7 @@
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/smp.h>
+#include <linux/bug.h>

#include <linux/hw_breakpoint.h>
/*
@@ -344,6 +345,38 @@ void release_bp_slot(struct perf_event *bp)
mutex_unlock(&nr_bp_mutex);
}

+static int __modify_bp_slot(struct perf_event *bp, u64 old_type)
+{
+ int err;
+
+ __release_bp_slot(bp, old_type);
+
+ err = __reserve_bp_slot(bp, bp->attr.bp_type);
+ if (err) {
+ /*
+ * Reserve the old_type slot back in case
+ * there's no space for the new type.
+ *
+ * This must succeed, because we just released
+ * the old_type slot in the __release_bp_slot
+ * call above. If not, something is broken.
+ */
+ WARN_ON(__reserve_bp_slot(bp, old_type));
+ }
+
+ return err;
+}
+
+static int modify_bp_slot(struct perf_event *bp, u64 old_type)
+{
+ int ret;
+
+ mutex_lock(&nr_bp_mutex);
+ ret = __modify_bp_slot(bp, old_type);
+ mutex_unlock(&nr_bp_mutex);
+ return ret;
+}
+
/*
* Allow the kernel debugger to reserve breakpoint slots without
* taking a lock using the dbg_* variant of for the reserve and
@@ -435,6 +468,7 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
u64 old_addr = bp->attr.bp_addr;
u64 old_len = bp->attr.bp_len;
int old_type = bp->attr.bp_type;
+ bool modify = attr->bp_type != old_type;
int err = 0;

/*
@@ -452,12 +486,9 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
bp->attr.bp_type = attr->bp_type;
bp->attr.bp_len = attr->bp_len;

- if (attr->disabled)
- goto end;
-
err = validate_hw_breakpoint(bp);
- if (!err)
- perf_event_enable(bp);
+ if (!err && modify)
+ err = modify_bp_slot(bp, old_type);

if (err) {
bp->attr.bp_addr = old_addr;
@@ -469,9 +500,10 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
return err;
}

-end:
- bp->attr.disabled = attr->disabled;
+ if (!attr->disabled)
+ perf_event_enable(bp);

+ bp->attr.disabled = attr->disabled;
return 0;
}
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
--
2.13.6
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