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Message-ID: <20090419091046.GA31192@elte.hu> Date: Sun, 19 Apr 2009 11:10:46 +0200 From: Ingo Molnar <mingo@...e.hu> To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> Cc: Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Frederic Weisbecker <fweisbec@...il.com>, Masami Hiramatsu <mhiramat@...hat.com> Subject: Re: [PATCH] x86 entry_64.S lockdep fix * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote: > * Steven Rostedt (rostedt@...dmis.org) wrote: > > > > On Fri, 17 Apr 2009, Mathieu Desnoyers wrote: > > > > > > I happened to have the following patch hanging around in my LTTng tree > > > for a while. Would it solve your problem by any chance ? I had to move > > > it a bit around in my patchset to put it before the nmi-safe int3 > > > handler patch I have, but it should apply correctly. > > > > > > > > > x86 entry_64.S lockdep fix > > > > > > Add missing lockdep irq on instrumentation to entry_64.S. > > > > > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> > > > --- > > > arch/x86/kernel/entry_64.S | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S > > > =================================================================== > > > --- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S 2009-04-17 17:44:18.000000000 -0400 > > > +++ linux-2.6-lttng/arch/x86/kernel/entry_64.S 2009-04-17 17:53:42.000000000 -0400 > > > @@ -1420,9 +1420,9 @@ ENTRY(paranoid_exit) > > > testl $3,CS(%rsp) > > > jnz paranoid_userspace > > > paranoid_swapgs: > > > - TRACE_IRQS_IRETQ 0 > > > SWAPGS_UNSAFE_STACK > > > paranoid_restore: > > > + TRACE_IRQS_IRETQ 0 > > > > This is buggy. If you go here via userspace, you just did a swapgs, and > > the %gs register (process context) is now zero. If you call kernel code > > that does anything with "current" you will crash the system. > > > > Argh, I should not have extracted my fix from my patchset and try to > reorder the patches that late in the day. Sorry, you are indeed right. > On the bright side, the patch I send earlier has never hit a repository. > Here is a more sensible version. > > > Add missing lockdep irq on instrumentation to entry_64.S. > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> > --- > arch/x86/kernel/entry_64.S | 3 +++ > 1 file changed, 3 insertions(+) > > Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S > =================================================================== > --- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S 2009-04-17 18:34:51.000000000 -0400 > +++ linux-2.6-lttng/arch/x86/kernel/entry_64.S 2009-04-18 23:41:28.000000000 -0400 > @@ -1422,7 +1422,10 @@ ENTRY(paranoid_exit) > paranoid_swapgs: > TRACE_IRQS_IRETQ 0 > SWAPGS_UNSAFE_STACK > + RESTORE_ALL 8 > + jmp irq_return > paranoid_restore: > + TRACE_IRQS_IRETQ 0 > RESTORE_ALL 8 > jmp irq_return > paranoid_userspace: Yeah - that is exactly the fix from Steve that i have queued up two days ago - see it attached below. Ingo ------------> >From 0300e7f1a525ae4e4ac05344624adf0e5f13ea52 Mon Sep 17 00:00:00 2001 From: Steven Rostedt <srostedt@...hat.com> Date: Fri, 17 Apr 2009 08:33:52 -0400 Subject: [PATCH] lockdep, x86: account for irqs enabled in paranoid_exit I hit the check_flags error of lockdep: WARNING: at kernel/lockdep.c:2893 check_flags+0x1a7/0x1d0() [...] hardirqs last enabled at (12567): [<ffffffff8026206a>] local_bh_enable+0xaa/0x110 hardirqs last disabled at (12569): [<ffffffff80610c76>] int3+0x16/0x40 softirqs last enabled at (12566): [<ffffffff80514d2b>] lock_sock_nested+0xfb/0x110 softirqs last disabled at (12568): [<ffffffff8058454e>] tcp_prequeue_process+0x2e/0xa0 The check_flags warning of lockdep tells me that lockdep thought interrupts were disabled, but they were really enabled. The numbers in the above parenthesis show the order of events: 12566: softirqs last enabled: lock_sock_nested 12567: hardirqs last enabled: local_bh_enable 12568: softirqs last disabled: tcp_prequeue_process 12566: hardirqs last disabled: int3 int3 is a breakpoint! Examining this further, I have CONFIG_NET_TCPPROBE enabled which adds break points into the kernel. The paranoid_exit of the return of int3 does not account for enabling interrupts on return to kernel. This code is a bit tricky since it is also used by the nmi handler (when lockdep is off), and we must be careful about the swapgs. We can not call kernel code after the swapgs has been performed. [ Impact: fix lockdep check_flags warning + self-turn-off ] Acked-by: Peter Zijlsta <a.p.zijlstra@...llo.nl> Signed-off-by: Steven Rostedt <rostedt@...dmis.org> Signed-off-by: Ingo Molnar <mingo@...e.hu> --- arch/x86/kernel/entry_64.S | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index a331ec3..38946c6 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1410,7 +1410,10 @@ ENTRY(paranoid_exit) paranoid_swapgs: TRACE_IRQS_IRETQ 0 SWAPGS_UNSAFE_STACK + RESTORE_ALL 8 + jmp irq_return paranoid_restore: + TRACE_IRQS_IRETQ 0 RESTORE_ALL 8 jmp irq_return paranoid_userspace: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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