Messages in this thread | | | Subject | Re: [PATCH] Move kfree_call_rcu() to slab_common.c | From | Rao Shoaib <> | Date | Thu, 21 Dec 2017 09:31:23 -0800 |
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On 12/21/2017 04:36 AM, Matthew Wilcox wrote: > On Thu, Dec 21, 2017 at 12:19:47AM -0800, rao.shoaib@oracle.com wrote: >> This patch moves kfree_call_rcu() and related macros out of rcu code. A new >> function __call_rcu_lazy() is created for calling __call_rcu() with the lazy >> flag. > Something you probably didn't know ... there are two RCU implementations > in the kernel; Tree and Tiny. It looks like you've only added > __call_rcu_lazy() to Tree and you'll also need to add it to Tiny. I left it out on purpose because the call in tiny is a little different
rcutiny.h:
static inline void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { call_rcu(head, func); }
tree.c:
void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, rcu_state_p, -1, 1); } EXPORT_SYMBOL_GPL(kfree_call_rcu);
If we want the code to be exactly same I can create a lazy version for tiny as well. However, I don not know where to move kfree_call_rcu() from it's current home in rcutiny.h though. Any thoughts ? > >> Also moving macros generated following checkpatch noise. I do not know >> how to silence checkpatch as there is nothing wrong. >> >> CHECK: Macro argument reuse 'offset' - possible side-effects? >> #91: FILE: include/linux/slab.h:348: >> +#define __kfree_rcu(head, offset) \ >> + do { \ >> + BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ >> + kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \ >> + } while (0) > What checkpatch is warning you about here is that somebody might call > > __kfree_rcu(p, a++); > > and this would expand into > > do { \ > BUILD_BUG_ON(!__is_kfree_rcu_offset(a++)); \ > kfree_call_rcu(p, (rcu_callback_t)(unsigned long)(a++)); \ > } while (0) > > which would increment 'a' twice, and cause pain and suffering. > > That's pretty unlikely usage of __kfree_rcu(), but I suppose it's not > impossible. We have various hacks to get around this kind of thing; > for example I might do this as:: > > #define __kfree_rcu(head, offset) \ > do { \ > unsigned long __o = offset; > BUILD_BUG_ON(!__is_kfree_rcu_offset(__o)); \ > kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(__o)); \ > } while (0) > > Now offset is only evaluated once per invocation of the macro. The other > two warnings are the same problem. > Thanks. I was not sure if I was required to fix the noise or based on inspection the noise could be ignored. I will make the change and resubmit.
Shoaib
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