Re-introduce task_work_cancel(), this time to cancel an actual callback
and not *any* callback pointing to a given function. This is going to be
needed for perf events event freeing.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 include/linux/task_work.h |  1 +
 kernel/task_work.c        | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index 89ee2cbf044b..58e42ef59580 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -37,6 +37,7 @@ int task_work_add(struct task_struct *task, struct callback_head *twork,
 struct callback_head *task_work_cancel_match(struct task_struct *task,
 	bool (*match)(struct callback_head *, void *data), void *data);
 struct callback_head *task_work_cancel_func(struct task_struct *, task_work_func_t);
+bool task_work_cancel(struct task_struct *, struct callback_head *twork);
 void task_work_run(void);
 
 static inline void exit_task_work(struct task_struct *task)
diff --git a/kernel/task_work.c b/kernel/task_work.c
index c1b4d3ba2590..9e85ac7632ae 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -136,6 +136,30 @@ task_work_cancel_func(struct task_struct *task, task_work_func_t func)
 	return task_work_cancel_match(task, task_work_func_match, func);
 }
 
+static bool task_work_match(struct callback_head *cb, void *data)
+{
+	return cb == data;
+}
+
+/**
+ * task_work_cancel - cancel a pending work added by task_work_add()
+ * @task: the task which should execute the work
+ * @func: the work to remove if queued
+ *
+ * Remove a callback from a task's queue if queued.
+ *
+ * RETURNS:
+ * True if the callback was queued and got cancelled, false otherwise.
+ */
+bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
+{
+	struct callback_head *ret;
+
+	ret = task_work_cancel_match(task, task_work_match, cb);
+
+	return ret == cb;
+}
+
 /**
  * task_work_run - execute the works added by task_work_add()
  *
-- 
2.44.0

Hi Frederic,

kernel test robot noticed the following build warnings:

[auto build test WARNING on perf-tools-next/perf-tools-next]
[also build test WARNING on tip/perf/core perf-tools/perf-tools linus/master acme/perf/core v6.9-rc1 next-20240328]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Frederic-Weisbecker/task_work-s-task_work_cancel-task_work_cancel_func/20240330-080207
base:   https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git perf-tools-next
patch link:    https://lore.kernel.org/r/20240329235812.18917-3-frederic%40kernel.org
patch subject: [PATCH 2/4] task_work: Introduce task_work_cancel() again
config: nios2-randconfig-r071-20240330 (https://download.01.org/0day-ci/archive/20240331/202403310406.TPrIela8-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240331/202403310406.TPrIela8-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202403310406.TPrIela8-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/task_work.c:155: warning: Function parameter or struct member 'cb' not described in 'task_work_cancel'
>> kernel/task_work.c:155: warning: Excess function parameter 'func' description in 'task_work_cancel'


vim +155 kernel/task_work.c

   143	
   144	/**
   145	 * task_work_cancel - cancel a pending work added by task_work_add()
   146	 * @task: the task which should execute the work
   147	 * @func: the work to remove if queued
   148	 *
   149	 * Remove a callback from a task's queue if queued.
   150	 *
   151	 * RETURNS:
   152	 * True if the callback was queued and got cancelled, false otherwise.
   153	 */
   154	bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
 > 155	{
   156		struct callback_head *ret;
   157	
   158		ret = task_work_cancel_match(task, task_work_match, cb);
   159	
   160		return ret == cb;
   161	}
   162	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki