On Thu, Nov 26, 2020 at 05:44:28PM +1100, Stephen Rothwell wrote:
> Hi all,
>
> After merging the rcu tree, today's linux-next build (htmldocs) produced
> these warnings:
>
> include/linux/rcupdate.h:872: warning: Excess function parameter 'ptr' description in 'kfree_rcu'
> include/linux/rcupdate.h:872: warning: Excess function parameter 'rhf' description in 'kfree_rcu'
>
> Introduced by commit
>
> beba8bdf2f16 ("rcu: Introduce kfree_rcu() single-argument macro")
Heh! The documentation isn't dealing at all well with this situation.
Would one of the docbook experts have some advice, keeping in mind
that kfree_rcu might have either one or two arguments?
Thanx, Paul
------------------------------------------------------------------------
/**
* kfree_rcu() - kfree an object after a grace period.
* @ptr: pointer to kfree for both single- and double-argument invocations.
* @rhf: the name of the struct rcu_head within the type of @ptr,
* but only for double-argument invocations.
*
* Many rcu callbacks functions just call kfree() on the base structure.
* These functions are trivial, but their size adds up, and furthermore
* when they are used in a kernel module, that module must invoke the
* high-latency rcu_barrier() function at module-unload time.
*
* The kfree_rcu() function handles this issue. Rather than encoding a
* function address in the embedded rcu_head structure, kfree_rcu() instead
* encodes the offset of the rcu_head structure within the base structure.
* Because the functions are not allowed in the low-order 4096 bytes of
* kernel virtual memory, offsets up to 4095 bytes can be accommodated.
* If the offset is larger than 4095 bytes, a compile-time error will
* be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
* either fall back to use of call_rcu() or rearrange the structure to
* position the rcu_head structure into the first 4096 bytes.
*
* 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 kvfree_rcu
