From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by oss.sgi.com (8.11.2/8.11.3) id fBK8xkD23335 for linux-mips-outgoing; Thu, 20 Dec 2001 00:59:46 -0800 Received: from mx.mips.com (mx.mips.com [206.31.31.226]) by oss.sgi.com (8.11.2/8.11.3) with SMTP id fBK8xUX23332 for ; Thu, 20 Dec 2001 00:59:30 -0800 Received: from newman.mips.com (ns-dmz [206.31.31.225]) by mx.mips.com (8.9.3/8.9.0) with ESMTP id XAA29298; Wed, 19 Dec 2001 23:58:50 -0800 (PST) Received: from copfs01.mips.com (copfs01 [192.168.205.101]) by newman.mips.com (8.9.3/8.9.0) with ESMTP id XAA22582; Wed, 19 Dec 2001 23:58:49 -0800 (PST) Received: from mips.com (copsun17 [192.168.205.27]) by copfs01.mips.com (8.11.4/8.9.0) with ESMTP id fBK7wfA05517; Thu, 20 Dec 2001 08:58:41 +0100 (MET) Message-ID: <3C219A3B.6DA93A75@mips.com> Date: Thu, 20 Dec 2001 08:58:51 +0100 From: Carsten Langgaard X-Mailer: Mozilla 4.75 [en] (X11; U; SunOS 5.7 sun4u) X-Accept-Language: en MIME-Version: 1.0 To: Jun Sun CC: linux-mips@oss.sgi.com Subject: Re: an old FPU context corruption problem when signal happens References: <3C21390A.FA23978D@mvista.com> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Sender: owner-linux-mips@oss.sgi.com Precedence: bulk Are you sure this hasn't been fix in the latest sources (2.4.16) ? I have send a patch to Ralf, which I believe solves a similar problem as you describe below. Ralf have you applied the patch ? /Carsten Jun Sun wrote: > This is an incomplete patch, attempting to fix an old fix FPU context > corruption problem with signal happens. > > The following scenario would cause many problems with current code: > > 1. process A runs and uses FPU > 2. Process A is switched out; Process B runs and uses FPU > 3. Process A runs again, but have not used FPU this time around > 4. Process A receives a signal. > 5. Process A's signal handler runs and uses FPU > 6. Process B runs again and uses FPU. > > At step 4, we have last_task_used_fpu being B, current->used_math being 1. > The current code would save B's FPU context to A's sc structure, but > does not mark owned_fp bits. > > At step 5, when A's sig handler first time uses FPU, FPU is enabled again. > > At step 6, when B tries to use FPU again, a lazy fpu switch happens. The > current FPU regs are stored into A's thread strucutre, effectively eraseing > previously stored A's FPU context before the sig handler starts. > > In addition, B finds its FPU reg values totally bogus when they are loaded > from B's thread structure, because the FPU regs were saved there. (See > step 4). > > This patch is meant for concept debugging. But it should be easy > to complete it: > > 1. support the two copy_fpu_context function. (note, need to differentiate > between CPU_HAS_FPU and !CPU_HAS_FPU cases) > 2. perhaps change ->sc_ownedfp to ->sc_used_fpu, which is really what > this flag means now. > > Any comments? > > Jun > > ------------------------------------------------------------------------ > > This is an incomplete patch, attempting to fix an old fix FPU context > corruption problem with signal happens. > > The following scenario would cause many problems with current code: > > 1. process A runs and uses FPU > 2. Process A is switched out; Process B runs and uses FPU > 3. Process A runs again, but have not used FPU this time around > 4. Process A receives a signal. > 5. Process A's signal handler runs and uses FPU > 6. Process B runs again and uses FPU. > > At step 4, we have last_task_used_fpu being B, current->used_math being 1. > The current code would save B's FPU context to A's sc structure, but > does not mark owned_fp bits. > > At step 5, when A's sig handler first time uses FPU, FPU is enabled again. > > At step 6, when B tries to use FPU again, a lazy fpu switch happens. The > current FPU regs are stored into A's thread strucutre, effectively eraseing > previously stored A's FPU context before the sig handler starts. > > In addition, B finds its FPU reg values totally bogus when they are loaded > from B's thread structure, because the FPU regs were saved there. (See > step 4). > > This patch is meant for concept debugging. But it should be easy > to complete it: > > 1. support the two copy_fpu_context function. (note, need to differentiate > between CPU_HAS_FPU and !CPU_HAS_FPU cases) > 2. perhaps change ->sc_ownedfp to ->sc_used_fpu, which is really what > this flag means now. > > Any comments? > > Jun > > diff -Nru linux.link/arch/mips/kernel/signal.c.orig linux.link/arch/mips/kernel/signal.c > --- linux.link/arch/mips/kernel/signal.c.orig Tue Nov 27 11:03:02 2001 > +++ linux.link/arch/mips/kernel/signal.c Wed Dec 19 16:28:08 2001 > @@ -222,8 +222,20 @@ > > err |= __get_user(owned_fp, &sc->sc_ownedfp); > if (owned_fp) { > - err |= restore_fp_context(sc); > - last_task_used_math = current; > + if ((last_task_used_match == NULL) || (last_task_used_math == current)) { > + /* if nobody owns FPU, or sig handler owns it, > + * we just restore FPU regs from sc to hardware */ > + err |= restore_fp_context(sc); > + last_task_used_math = current; > + enable_fpu(); > + } else { > + /* we copy FPU values from sc to task structure */ > + err |= copy_fpu_context_from_sigcontext(current, sc); > + disable_fpu(); > + } > + > + /* in either case, we need to set the used flag */ > + current->used_math = 1; > } > > return err; > @@ -352,13 +364,25 @@ > err |= __put_user(regs->cp0_cause, &sc->sc_cause); > err |= __put_user(regs->cp0_badvaddr, &sc->sc_badvaddr); > > - owned_fp = (current == last_task_used_math); > - err |= __put_user(owned_fp, &sc->sc_ownedfp); > + /* if we ever used FPU, we need to get FPU regs to sc */ > + if (current->used_math) { > + > + if (current == last_task_used_math) { > + /* if we own FPU now, just save fpu to sc directly */ > + enable_fpu(); > + err |= save_fp_context(sc); > + } else { > + /* otherwise, we need copy fpu regs from current task > + * structure to sc structre. > + */ > + err |= copy_fpu_context_to_sigcontext(current, sc); > + } > + > + /* put remember that we have valid FPU regs in sc */ > + err |= __put_user(current->used_math, &sc->sc_ownedfp); > > - if (current->used_math) { /* fp is active. */ > - enable_fpu(); > - err |= save_fp_context(sc); > - last_task_used_math = NULL; > + /* we now pretend we have never used FPU before we start sig > + * handler */ > regs->cp0_status &= ~ST0_CU1; > current->used_math = 0; > } -- _ _ ____ ___ Carsten Langgaard Mailto:carstenl@mips.com |\ /|||___)(___ MIPS Denmark Direct: +45 4486 5527 | \/ ||| ____) Lautrupvang 4B Switch: +45 4486 5555 TECHNOLOGIES 2750 Ballerup Fax...: +45 4486 5556 Denmark http://www.mips.com