| Message ID | 20250317092945.764490535@linutronix.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | genirq/msi: Spring cleaning | expand |
On Mon, 2025-03-17 at 14:29 +0100, Thomas Gleixner wrote: [...] > +/* > + * Only for situations where an allocation is handed in to another > function > + * and consumed by that function on success. > + * > + * struct foo *f __free(kfree) = kzalloc(sizeof(*f), > GFP_KERNEL); > + * > + * setup(f); > + * if (some_condition) > + * return -EINVAL; > + * .... > + * ret = bar(f); > + * if (!ret) > + * retain_ptr(f); > + * return ret; > + */ > +#define retain_ptr(p) \ > + __get_and_null(p, NULL) This doesn't score very highly on the Rusty API design scale because it can be used anywhere return_ptr() should be used. To force the distinction between the two cases at the compiler level, should there be a cast to void in the above to prevent using the return value? Regards, James
On Mon, Mar 17 2025 at 09:57, James Bottomley wrote: > On Mon, 2025-03-17 at 14:29 +0100, Thomas Gleixner wrote: >> +#define retain_ptr(p) \ >> + __get_and_null(p, NULL) > > This doesn't score very highly on the Rusty API design scale because it > can be used anywhere return_ptr() should be used. To force the > distinction between the two cases at the compiler level, should there > be a cast to void in the above to prevent using the return value? Indeed. Delta patch below seems to do the trick. Thanks, tglx --- diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h index 6537f8dfe1bb..859b06d4ad7a 100644 --- a/include/linux/cleanup.h +++ b/include/linux/cleanup.h @@ -231,8 +231,7 @@ const volatile void * __must_check_fn(const volatile void *val) * retain_ptr(f); * return ret; */ -#define retain_ptr(p) \ - __get_and_null(p, NULL) +#define retain_ptr(p) ((void)__get_and_null(p, NULL)) /* * DEFINE_CLASS(name, type, exit, init, init_args...):
--- a/include/linux/cleanup.h +++ b/include/linux/cleanup.h @@ -216,6 +216,23 @@ const volatile void * __must_check_fn(co #define return_ptr(p) return no_free_ptr(p) +/* + * Only for situations where an allocation is handed in to another function + * and consumed by that function on success. + * + * struct foo *f __free(kfree) = kzalloc(sizeof(*f), GFP_KERNEL); + * + * setup(f); + * if (some_condition) + * return -EINVAL; + * .... + * ret = bar(f); + * if (!ret) + * retain_ptr(f); + * return ret; + */ +#define retain_ptr(p) \ + __get_and_null(p, NULL) /* * DEFINE_CLASS(name, type, exit, init, init_args...):
In cases where an allocation is consumed by another function, the allocation needs to be retained on success or freed on failure. The code pattern is usually: struct foo *f = kzalloc(sizeof(*f), GFP_KERNEL); struct bar *b; ,,, // Initialize f ... if (ret) goto free; ... bar = bar_create(f); if (!bar) { ret = -ENOMEM; goto free; } ... return 0; free: kfree(f); return ret; This prevents using __free(kfree) on @f because there is no canonical way to tell the cleanup code that the allocation should not be freed. Abusing no_free_ptr() by force ignoring the return value is not really a sensible option either. Provide an explicit macro retain_ptr(), which NULLs the cleanup pointer. That makes it easy to analyze and reason about. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Cc: Peter Zijlstra <peterz@infradead.org> --- include/linux/cleanup.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)