linux-kernel - [PATCH] x86/traps: Weaken context tracking entry assertions

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Message-Id: <c81faf3916346c0e04346c441392974f49cd7184.1440133286.git.luto@kernel.org>
Date:	Thu, 20 Aug 2015 22:03:21 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Brian Gerst <brgerst@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH] x86/traps: Weaken context tracking entry assertions

We were asserting that we were all the way in CONTEXT_KERNEL when
exception handlers were called.  While having this be true is, I
think, a nice goal (or maybe a variant in which we assert that we're
in CONTEXT_KERNEL or some new IRQ context), we're not quite there.

In particular, if an IRQ interrupts the SYSCALL prologue and the IRQ
handler in turn causes an exception, the exception entry will be
called in RCU IRQ mode but with CONTEXT_USER.

This is okay (nothing goes wrong), but until we fix up the SYSCALL
prologue, we need to avoid warning.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/traps.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 86a82eafb96f..45e8d9891fa3 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -112,7 +112,7 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 void ist_enter(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
-		CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+		rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	} else {
 		/*
 		 * We might have interrupted pretty much anything.  In
@@ -282,7 +282,7 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
 {
 	siginfo_t info;
 
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 
 	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
 			NOTIFY_STOP) {
@@ -364,7 +364,7 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 	const struct bndcsr *bndcsr;
 	siginfo_t *info;
 
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	if (notify_die(DIE_TRAP, "bounds", regs, error_code,
 			X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
 		return;
@@ -442,7 +442,7 @@ do_general_protection(struct pt_regs *regs, long error_code)
 {
 	struct task_struct *tsk;
 
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	conditional_sti(regs);
 
 	if (v8086_mode(regs)) {
@@ -496,7 +496,7 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
 		return;
 
 	ist_enter(regs);
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
 	if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
 				SIGTRAP) == NOTIFY_STOP)
@@ -729,14 +729,14 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 
 dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code)
 {
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	math_error(regs, error_code, X86_TRAP_MF);
 }
 
 dotraplinkage void
 do_simd_coprocessor_error(struct pt_regs *regs, long error_code)
 {
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	math_error(regs, error_code, X86_TRAP_XF);
 }
 
@@ -749,7 +749,7 @@ do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
 dotraplinkage void
 do_device_not_available(struct pt_regs *regs, long error_code)
 {
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	BUG_ON(use_eager_fpu());
 
 #ifdef CONFIG_MATH_EMULATION
@@ -775,7 +775,7 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 {
 	siginfo_t info;
 
-	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
+	rcu_lockdep_assert(rcu_is_watching(), "entry code didn't wake RCU");
 	local_irq_enable();
 
 	info.si_signo = SIGILL;
-- 
2.4.3

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