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x86, traps: Fix ist_enter from userspace 

context_tracking_user_exit() has no effect if in_interrupt() returns true,
so ist_enter() didn't work.  Fix it by calling exception_enter(), and thus
context_tracking_user_exit(), before incrementing the preempt count.

This also adds an assertion that will catch the problem reliably if
CONFIG_PROVE_RCU=y to help prevent the bug from being reintroduced.

Link: http://lkml.kernel.org/r/261ebee6aee55a4724746d0d7024697013c40a08.1422709102.git.luto@amacapital.net
Fixes: 9592747538 x86, traps: Track entry into and exit from IST context
Reported-and-tested-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
This commit is contained in:
Andy Lutomirski 2015-01-31 04:53:53 -08:00
parent 772a9aca12
commit b926e6f61a
1 changed files with 18 additions and 7 deletions
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25
arch/x86/kernel/traps.c
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@ -110,15 +110,11 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
enum ctx_state ist_enter(struct pt_regs *regs)
{
/*
* We are atomic because we're on the IST stack (or we're on x86_32,
* in which case we still shouldn't schedule.
*/
preempt_count_add(HARDIRQ_OFFSET);
enum ctx_state prev_state;
if (user_mode_vm(regs)) {
/* Other than that, we're just an exception. */
return exception_enter();
prev_state = exception_enter();
} else {
/*
* We might have interrupted pretty much anything. In
@ -127,12 +123,27 @@ enum ctx_state ist_enter(struct pt_regs *regs)
* but we need to notify RCU.
*/
rcu_nmi_enter();
return IN_KERNEL; /* the value is irrelevant. */
prev_state = IN_KERNEL; /* the value is irrelevant. */
}
/*
* We are atomic because we're on the IST stack (or we're on x86_32,
* in which case we still shouldn't schedule).
*
* This must be after exception_enter(), because exception_enter()
* won't do anything if in_interrupt() returns true.
*/
preempt_count_add(HARDIRQ_OFFSET);
/* This code is a bit fragile. Test it. */
rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work");
return prev_state;
}
void ist_exit(struct pt_regs *regs, enum ctx_state prev_state)
{
/* Must be before exception_exit. */
preempt_count_sub(HARDIRQ_OFFSET);
if (user_mode_vm(regs))