workqueue: clean up WORK_* constant types, clarify masking

Dave Airlie reports that gcc-13.1.1 has started complaining about some
of the workqueue code in 32-bit arm builds:

  kernel/workqueue.c: In function ‘get_work_pwq’:
  kernel/workqueue.c:713:24: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
    713 |                 return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
        |                        ^
  [ ... a couple of other cases ... ]

and while it's not immediately clear exactly why gcc started complaining
about it now, I suspect it's some C23-induced enum type handlign fixup in
gcc-13 is the cause.

Whatever the reason for starting to complain, the code and data types
are indeed disgusting enough that the complaint is warranted.

The wq code ends up creating various "helper constants" (like that
WORK_STRUCT_WQ_DATA_MASK) using an enum type, which is all kinds of
confused.  The mask needs to be 'unsigned long', not some unspecified
enum type.

To make matters worse, the actual "mask and cast to a pointer" is
repeated a couple of times, and the cast isn't even always done to the
right pointer, but - as the error case above - to a 'void *' with then
the compiler finishing the job.

That's now how we roll in the kernel.

So create the masks using the proper types rather than some ambiguous
enumeration, and use a nice helper that actually does the type
conversion in one well-defined place.

Incidentally, this magically makes clang generate better code.  That,
admittedly, is really just a sign of clang having been seriously
confused before, and cleaning up the typing unconfuses the compiler too.

Reported-by: Dave Airlie <airlied@gmail.com>
Link: https://lore.kernel.org/lkml/CAPM=9twNnV4zMCvrPkw3H-ajZOH-01JVh_kDrxdPYQErz8ZTdA@mail.gmail.com/
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4666a1a92a31b2..c913e333cce8ea 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -705,12 +705,17 @@ static void clear_work_data(struct work_struct *work)
 	set_work_data(work, WORK_STRUCT_NO_POOL, 0);
 }
 
+static inline struct pool_workqueue *work_struct_pwq(unsigned long data)
+{
+	return (struct pool_workqueue *)(data & WORK_STRUCT_WQ_DATA_MASK);
+}
+
 static struct pool_workqueue *get_work_pwq(struct work_struct *work)
 {
 	unsigned long data = atomic_long_read(&work->data);
 
 	if (data & WORK_STRUCT_PWQ)
-		return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
+		return work_struct_pwq(data);
 	else
 		return NULL;
 }
@@ -738,8 +743,7 @@ static struct worker_pool *get_work_pool(struct work_struct *work)
 	assert_rcu_or_pool_mutex();
 
 	if (data & WORK_STRUCT_PWQ)
-		return ((struct pool_workqueue *)
-			(data & WORK_STRUCT_WQ_DATA_MASK))->pool;
+		return work_struct_pwq(data)->pool;
 
 	pool_id = data >> WORK_OFFQ_POOL_SHIFT;
 	if (pool_id == WORK_OFFQ_POOL_NONE)
@@ -760,8 +764,7 @@ static int get_work_pool_id(struct work_struct *work)
 	unsigned long data = atomic_long_read(&work->data);
 
 	if (data & WORK_STRUCT_PWQ)
-		return ((struct pool_workqueue *)
-			(data & WORK_STRUCT_WQ_DATA_MASK))->pool->id;
+		return work_struct_pwq(data)->pool->id;
 
 	return data >> WORK_OFFQ_POOL_SHIFT;
 }