| Message ID | 1335199347-13926-5-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | Accepted |
| Commit | d8169d4c369e8aa2fda10df705a4957331b5a4db |
| Headers | show |
On Mon, 2012-04-23 at 09:42 -0700, Paul E. McKenney wrote: > Currently, __kfree_rcu() is implemented as an inline function, and > contains a BUILD_BUG_ON() that malfunctions if __kfree_rcu() is compiled > as an out-of-line function. Unfortunately, there are compiler settings > (e.g., -O0) that can result in __kfree_rcu() being compiled out of line, > resulting in annoying build breakage. This commit therefore converts > both __kfree_rcu() and __is_kfree_rcu_offset() from inline functions to > macros to prevent such misbehavior on the part of the compiler. The kernel very explicitly doesn't support being compiled with -O0, so this is a non-issue, I think you can make it work if you add -finline-functions. I'd drop this, either make the entire kernel compile or don't bother.
On Thursday 2012-04-26 14:48, Peter Zijlstra wrote: >On Mon, 2012-04-23 at 09:42 -0700, Paul E. McKenney wrote: >> Currently, __kfree_rcu() is implemented as an inline function, and >> contains a BUILD_BUG_ON() that malfunctions if __kfree_rcu() is compiled >> as an out-of-line function. Unfortunately, there are compiler settings >> (e.g., -O0) that can result in __kfree_rcu() being compiled out of line, >> resulting in annoying build breakage. This commit therefore converts >> both __kfree_rcu() and __is_kfree_rcu_offset() from inline functions to >> macros to prevent such misbehavior on the part of the compiler. > >The kernel very explicitly doesn't support being compiled with -O0, so >this is a non-issue, I think you can make it work if you add >-finline-functions. > >I'd drop this, either make the entire kernel compile or don't bother. It was not originally meant to make the entire kernel compile with -O0, but only select modules/.c files. That, or __always_inline just does not always inline.
On Thu, 2012-04-26 at 15:29 +0200, Jan Engelhardt wrote: > On Thursday 2012-04-26 14:48, Peter Zijlstra wrote: > >On Mon, 2012-04-23 at 09:42 -0700, Paul E. McKenney wrote: > >> Currently, __kfree_rcu() is implemented as an inline function, and > >> contains a BUILD_BUG_ON() that malfunctions if __kfree_rcu() is compiled > >> as an out-of-line function. Unfortunately, there are compiler settings > >> (e.g., -O0) that can result in __kfree_rcu() being compiled out of line, > >> resulting in annoying build breakage. This commit therefore converts > >> both __kfree_rcu() and __is_kfree_rcu_offset() from inline functions to > >> macros to prevent such misbehavior on the part of the compiler. > > > >The kernel very explicitly doesn't support being compiled with -O0, so > >this is a non-issue, I think you can make it work if you add > >-finline-functions. > > > >I'd drop this, either make the entire kernel compile or don't bother. > > It was not originally meant to make the entire kernel compile with -O0, > but only select modules/.c files. Same problem, who cares about select modules/.c files? Why should they have different rules? > That, or __always_inline just does not always inline. It does indeed not without -finline-functions.
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 20fb776..d5dfb10 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -922,6 +922,21 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset) kfree_call_rcu(head, (rcu_callback)offset); } +/* + * Does the specified offset indicate that the corresponding rcu_head + * structure can be handled by kfree_rcu()? + */ +#define __is_kfree_rcu_offset(offset) ((offset) < 4096) + +/* + * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. + */ +#define __kfree_rcu(head, offset) \ + do { \ + BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ + call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ + } while (0) + /** * kfree_rcu() - kfree an object after a grace period. * @ptr: pointer to kfree @@ -944,6 +959,9 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset) * * Note that the allowable offset might decrease in the future, for example, * to allow something like kmem_cache_free_rcu(). + * + * The BUILD_BUG_ON check must not involve any function calls, hence the + * checks are done in macros here. */ #define kfree_rcu(ptr, rcu_head) \ __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))