Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932722Ab2KWGxR (ORCPT ); Fri, 23 Nov 2012 01:53:17 -0500 Received: from mail-da0-f46.google.com ([209.85.210.46]:53072 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932397Ab2KWGxO (ORCPT ); Fri, 23 Nov 2012 01:53:14 -0500 Date: Thu, 22 Nov 2012 22:50:02 -0800 From: Anton Vorontsov To: Alexander Shiyan Cc: Andrew Morton , linaro-kernel@lists.linaro.org, Russell King , patches@linaro.org, linux-kernel@vger.kernel.org, John Stultz , Jason Wessel , kernel-team@android.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 10/10] ARM: FIQ: Get rid of init_FIQ() Message-ID: <20121123065002.GB27827@lizard> References: <20121123003849.GA973@lizard.mcd25758.sjc.wayport.net> <1353642030.851395840@f20.mail.ru> <20121123055328.GA21566@lizard> <1353652071.755665772@f76.mail.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1353652071.755665772@f76.mail.ru> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2556 Lines: 63 On Fri, Nov 23, 2012 at 10:27:51AM +0400, Alexander Shiyan wrote: > > On Fri, Nov 23, 2012 at 07:40:30AM +0400, Alexander Shiyan wrote: > > [...] > > > > static unsigned long no_fiq_insn; > > > > +static int got_no_fiq_insn; > > > > @@ -78,11 +79,14 @@ void show_fiq_list(struct seq_file *p, int prec) > > > > > > > > void set_fiq_handler(void *start, unsigned int length) > > > > { > > > > -#if defined(CONFIG_CPU_USE_DOMAINS) > > > > - memcpy((void *)0xffff001c, start, length); > > > > -#else > > > > - memcpy(vectors_page + 0x1c, start, length); > > > > + unsigned long *addr = (void *)0xffff001c; > > > > + > > > > +#ifndef CONFIG_CPU_USE_DOMAINS > > > > + addr = vectors_page + 0x1c; > > > > #endif > > > > + if (!cmpxchg(&got_no_fiq_insn, 0, 1)) > > > > + no_fiq_insn = *addr; > > > > + memcpy(addr, start, length); > > > > flush_icache_range(0xffff001c, 0xffff001c + length); > > > > if (!vectors_high()) > > > > flush_icache_range(0x1c, 0x1c + length); > > > > @@ -126,8 +130,3 @@ EXPORT_SYMBOL(__set_fiq_regs); /* defined in fiqasm.S */ > > > > - > > > > -void __init init_FIQ(void) > > > > -{ > > > > - no_fiq_insn = *(unsigned long *)0xffff001c; > > > > > > it seems that this is wrong. In this case we have an uninitialized variable and > > > sequential call claim_fiq and release_fiq could be fatal. FIXME please. > > > > Um... I don't think I understand, can you please elaborate? > > OK, I'll try to explain it. > At the end of the release_fiq function we have a call fiq_op. For the default > handler - is a fiq_def_op function, and we call this function with the option > "relinquish = 0", i.e. we want to restore old fiq_handler. But if we do not call > set_fiq_handler never before, we will have an uninitialized no_fiq_insn variable. It should not matter when or in what order anyone calls the set_fiq_handler(), since it stores "no FIQ instruction" into no_fiq_insn at its first invocation: if (!cmpxchg(&got_no_fiq_insn, 0, 1)) no_fiq_insn = *addr; If we never called set_fiq_handler() before, during release_fiq() we'll: 1. Copy the initial instruction from the vector page to 'no_fiq_insn'; 2. Copy the initial instruction from 'no_fiq_insn' to the vector page; So no_fiq_insn gets initialized, then we just instantly write the same value back. Thanks, Anton. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/