Messages in this thread |  | | Date | Sun, 7 Jun 2009 19:52:11 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] kmemcheck: move hook before preempt_conditional_sti() |
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* Vegard Nossum <vegard.nossum@gmail.com> wrote:
> 2009/6/7 Ingo Molnar <mingo@elte.hu>: > > > > * Vegard Nossum <vegard.nossum@gmail.com> wrote: > > > >> There are actually two problems here: > >> > >> 1. We absolutely cannot enable IRQs in case the fault was caused by > >> kmemcheck. > >> > >> 2. We cannot enable preemption and then return from the debug handler > >> without disabling preemption afterwards. > >> > >> The problem seems to be a merge fallout between three commits: > >> > >> commit 3d2a71a596bd9c761c8487a2178e95f8a61da083 > >> Author: Alexander van Heukelum <heukelum@fastmail.fm> > >> Date: Tue Sep 30 18:41:37 2008 +0200 > >> > >> x86, traps: converge do_debug handlers > >> > >> commit 08d68323d1f0c34452e614263b212ca556dae47f > >> Author: K.Prasad <prasad@linux.vnet.ibm.com> > >> Date: Mon Jun 1 23:44:08 2009 +0530 > >> > >> hw-breakpoints: modifying generic debug exception to use thread-specific deb > >> > >> commit 787ecfaa503dc63ff1831ddc74b15dad49bace1d > >> Author: Vegard Nossum <vegard.nossum@gmail.com> > >> Date: Fri Apr 4 00:53:23 2008 +0200 > >> > >> x86: add hooks for kmemcheck > >> > >> I encourage the kprobe developers to check whether their code is correct > >> as it stands in current tip/master. Also, comments on this particular > >> change is welcome. > >> > >> Reported-by: Ingo Molnar <mingo@elte.hu> > >> Cc: Alexander van Heukelum <heukelum@fastmail.fm> > >> Cc: K.Prasad <prasad@linux.vnet.ibm.com> > >> Cc: Alan Stern <stern@rowland.harvard.edu> > >> Cc: Frederic Weisbecker <fweisbec@gmail.com> > >> Cc: Pekka Enberg <penberg@cs.helsinki.fi> > >> Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com> > >> --- > >> arch/x86/kernel/traps.c | 8 ++++---- > >> 1 files changed, 4 insertions(+), 4 deletions(-) > > > >> > >> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > >> index c8a7f87..a898c6b 100644 > >> --- a/arch/x86/kernel/traps.c > >> +++ b/arch/x86/kernel/traps.c > >> @@ -550,6 +550,10 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) > >> SIGTRAP) == NOTIFY_STOP) > >> return; > >> > >> + /* Catch kmemcheck conditions first of all! */ > >> + if ((dr6 & DR_STEP) && kmemcheck_trap(regs)) > >> + return; > >> + > >> /* It's safe to allow irq's after DR6 has been saved */ > >> preempt_conditional_sti(regs); > >> > >> @@ -559,10 +563,6 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) > >> return; > >> } > >> > >> - /* Catch kmemcheck conditions first of all! */ > >> - if ((dr6 & DR_STEP) && kmemcheck_trap(regs)) > >> - return; > >> - > >> /* > >> * Single-stepping through system calls: ignore any exceptions in > >> * kernel space, but re-enable TF when returning to user mode. > > > > Yeah - this could solve the crash i saw. Mind sending a pull request > > too? > > It did solve it, I tested it :-D > > This patch was against tip/master; tip/kmemcheck does not have the > problem. I think it might have been introduced in this merge: > > commit 85b9b2801e46a147330b8a0f321bc40342ff5b4c > Merge: bf8d9b3... 7387400... > Author: Ingo Molnar <mingo@elte.hu> > Date: Thu Jun 4 13:56:43 2009 +0200 > > Merge branch 'tracing/hw-breakpoints' > > Conflicts: > arch/x86/Kconfig > arch/x86/kernel/traps.c > kernel/Makefile
Ah. kmemcheck + hw-breakpoints interaction. Fun.
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