Messages in this thread | | | Date | Tue, 10 Jan 2023 13:46:37 +0100 | Subject | Re: [Intel-gfx] [RFC DO NOT MERGE] treewide: use __xchg in most obvious places | From | Andrzej Hajda <> |
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On 10.01.2023 12:07, Andy Shevchenko wrote: > On Tue, Jan 10, 2023 at 11:53:06AM +0100, Andrzej Hajda wrote: >> This patch tries to show usability of __xchg helper. >> It is not intended to be merged, but I can convert >> it to proper patchset if necessary. >> >> There are many more places where __xchg can be used. >> This demo shows the most spectacular cases IMHO: >> - previous value is returned from function, >> - temporary variables are in use. >> >> As a result readability is much better and diffstat is quite >> nice, less local vars to look at. >> In many cases whole body of functions is replaced >> with __xchg(ptr, val), so as further refactoring the whole >> function can be removed and __xchg can be called directly. > > ... > >> arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, >> struct pt_regs *regs) >> { >> - unsigned long orig_ret_vaddr; >> - >> - orig_ret_vaddr = regs->ARM_lr; >> - /* Replace the return addr with trampoline addr */ >> - regs->ARM_lr = trampoline_vaddr; >> - return orig_ret_vaddr; >> + return __xchg(®s->ARM_lr, trampoline_vaddr); >> } > > If it's not a callback, the entire function can be killed. > And this is a good example of the function usage. > OTOH, these places might have a side effect (if it's in deep CPU > handlers), means we need to do this carefully. > > ... > >> static inline void *qed_chain_produce(struct qed_chain *p_chain) >> { >> - void *p_ret = NULL, *p_prod_idx, *p_prod_page_idx; >> + void *p_prod_idx, *p_prod_page_idx; >> >> if (is_chain_u16(p_chain)) { >> if ((p_chain->u.chain16.prod_idx & >> @@ -390,11 +391,8 @@ static inline void *qed_chain_produce(struct qed_chain *p_chain) >> p_chain->u.chain32.prod_idx++; >> } >> >> - p_ret = p_chain->p_prod_elem; >> - p_chain->p_prod_elem = (void *)(((u8 *)p_chain->p_prod_elem) + >> - p_chain->elem_size); >> - >> - return p_ret; >> + return __xchg(&p_chain->p_prod_elem, >> + (void *)(((u8 *)p_chain->p_prod_elem) + p_chain->elem_size)); > > Wondering if you still need a (void *) casting after the change. Ditto for the > rest of similar cases.
IMHO it is not needed also before the change and IIRC gcc has an extension which allows to drop (u8 *) cast as well [1].
[1]: https://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html
> >> } > > ... > > Btw, is it done by coccinelle? If no, why not providing the script? >
Yes I have used cocci. My cocci skills are far from perfect, so I did not want to share my dirty code, but this is nothing secret:
@r1@ expression x, v; local idexpression p; @@ - p = x; - x = v; - return p; + return __xchg(&x, v);
@depends on r1@ expression e; @@ __xchg( - &*e, + e, ...)
@depends on r1@ expression t; @@ - if (t) { + if (t) return __xchg(...); - }
@depends on r1@ type t; identifier p; expression e; @@ ( - t p; | - t p = e; ) ... when != p
Regards Andrzej
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