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Subject[PATCH] uprobes: Add uprobe_task->dup_work/dup_addr
uprobe_task->vaddr is a bit strange. First of all it is not really
needed, we can move it into arch_uprobe_task. The generic code uses
it only to pass the additional argument to arch_uprobe_pre_xol(),
and since it is always equal to instruction_pointer() this looks
even more strange.

And both utask->vaddr and and utask->autask have the same scope,
they only have the meaning when the task executes the probed insn
out-of-line. This means it is safe to reuse both in UTASK_RUNNING
state.

OTOH, it is also used by uprobe_copy_process() and dup_xol_work()
for another purpose, this doesn't look clean and doesn't allow to
move this member into arch_uprobe_task.

This patch adds the union with 2 anonymous structs into uprobe_task.

The first struct is autask + vaddr, this way we "almost" move vaddr
into autask.

The second struct has 2 new members for uprobe_copy_process() paths:
->dup_addr which can be used instead ->vaddr, and ->dup_work which
can be used to avoid kmalloc() and simplify the code.

Note that this union will likely have another member(s), we need
something like "private_data_for_handlers" so that the tracing
handlers could use it to communicate with call_fetch() methods.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/linux/uprobes.h | 21 ++++++++++++++++-----
kernel/events/uprobes.c | 16 ++++------------
2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 319eae7..366b8b2 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -26,6 +26,7 @@

#include <linux/errno.h>
#include <linux/rbtree.h>
+#include <linux/types.h>

struct vm_area_struct;
struct mm_struct;
@@ -72,14 +73,24 @@ enum uprobe_task_state {
*/
struct uprobe_task {
enum uprobe_task_state state;
- struct arch_uprobe_task autask;

- struct return_instance *return_instances;
- unsigned int depth;
- struct uprobe *active_uprobe;
+ union {
+ struct {
+ struct arch_uprobe_task autask;
+ unsigned long vaddr;
+ };
+
+ struct {
+ struct callback_head dup_work;
+ unsigned long dup_addr;
+ };
+ };

+ struct uprobe *active_uprobe;
unsigned long xol_vaddr;
- unsigned long vaddr;
+
+ struct return_instance *return_instances;
+ unsigned int depth;
};

/*
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 24b7d6c..2546a7b 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1403,12 +1403,10 @@ static void uprobe_warn(struct task_struct *t, const char *msg)

static void dup_xol_work(struct callback_head *work)
{
- kfree(work);
-
if (current->flags & PF_EXITING)
return;

- if (!__create_xol_area(current->utask->vaddr))
+ if (!__create_xol_area(current->utask->dup_addr))
uprobe_warn(current, "dup xol area");
}

@@ -1419,7 +1417,6 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
{
struct uprobe_task *utask = current->utask;
struct mm_struct *mm = current->mm;
- struct callback_head *work;
struct xol_area *area;

t->utask = NULL;
@@ -1441,14 +1438,9 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
if (mm == t->mm)
return;

- /* TODO: move it into the union in uprobe_task */
- work = kmalloc(sizeof(*work), GFP_KERNEL);
- if (!work)
- return uprobe_warn(t, "dup xol area");
-
- t->utask->vaddr = area->vaddr;
- init_task_work(work, dup_xol_work);
- task_work_add(t, work, true);
+ t->utask->dup_addr = area->vaddr;
+ init_task_work(&t->utask->dup_work, dup_xol_work);
+ task_work_add(t, &t->utask->dup_work, true);
}

/*
--
1.5.5.1



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