Messages in this thread | | | Date | Sun, 7 Jun 2009 19:25:13 +0200 | Subject | Re: [PATCH] kmemcheck: move hook before preempt_conditional_sti() | From | Vegard Nossum <> |
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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
Vegard
-- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036 -- 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/
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