From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrzej Hajda Date: Tue, 10 Jan 2023 12:46:37 +0000 Subject: Re: [Intel-gfx] [RFC DO NOT MERGE] treewide: use __xchg in most obvious places Message-Id: <1bfae3d0-8c0b-ea83-7184-db847a4a969f@intel.com> List-Id: References: <20230110105306.3973122-1-andrzej.hajda@intel.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andy Shevchenko Cc: Mark Rutland , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , dri-devel@lists.freedesktop.org, linux-mips@vger.kernel.org, sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-snps-arc@lists.infradead.org, Boqun Feng , linux-xtensa@linux-xtensa.org, Arnd Bergmann , intel-gfx@lists.freedesktop.org, linux-m68k@lists.linux-m68k.org, openrisc@lists.librecores.org, loongarch@lists.linux.dev, Rodrigo Vivi , linux-arm-kernel@lists.infradead.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Vetter , linux-alpha@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org 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