[PATCH] x86_64: Don't schedule on exception stack on preemptive kernels

Extends an earlier patch from John Blackwood to more exception handlers
that also run on the exception stacks.

Expand the use of preempt_conditional_{sti,cli} to all cases where
interrupts are to be re-enabled during exception handling while running
on an IST stack.

Based on original patch from Jan Beulich.

Cc: John Blackwood <john.blackwood@ccur.com>
Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 4 deletions

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 6b87268c5c2e..cea335e8746c 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -102,6 +102,8 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 {
         if (regs->eflags & X86_EFLAGS_IF)
                 local_irq_disable();
+        /* Make sure to not schedule here because we could be running
+           on an exception stack. */
         preempt_enable_no_resched();
 }
 
@@ -483,8 +485,6 @@ static void __kprobes do_trap(int trapnr, int signr, char *str,
 {
         struct task_struct *tsk = current;
 
-        conditional_sti(regs);
-
         tsk->thread.error_code = error_code;
         tsk->thread.trap_no = trapnr;
 
@@ -521,6 +521,7 @@ asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
         if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
                                                         == NOTIFY_STOP) \
                 return; \
+        conditional_sti(regs);                                          \
         do_trap(trapnr, signr, str, regs, error_code, NULL); \
 }
 
@@ -535,6 +536,7 @@ asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
         if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
                                                         == NOTIFY_STOP) \
                 return; \
+        conditional_sti(regs);                                          \
         do_trap(trapnr, signr, str, regs, error_code, &info); \
 }
 
@@ -548,7 +550,17 @@ DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
 DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
 DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
 DO_ERROR(18, SIGSEGV, "reserved", reserved)
-DO_ERROR(12, SIGBUS,  "stack segment", stack_segment)
+
+/* Runs on IST stack */
+asmlinkage void do_stack_segment(struct pt_regs *regs, long error_code)
+{
+        if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
+                        12, SIGBUS) == NOTIFY_STOP)
+                return;
+        preempt_conditional_sti(regs);
+        do_trap(12, SIGBUS, "stack segment", regs, error_code, NULL);
+        preempt_conditional_cli(regs);
+}
 
 asmlinkage void do_double_fault(struct pt_regs * regs, long error_code)
 {
@@ -682,8 +694,9 @@ asmlinkage void __kprobes do_int3(struct pt_regs * regs, long error_code)
         if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP) == NOTIFY_STOP) {
                 return;
         }
+        preempt_conditional_sti(regs);
         do_trap(3, SIGTRAP, "int3", regs, error_code, NULL);
-        return;
+        preempt_conditional_cli(regs);
 }
 
 /* Help handler running on IST stack to switch back to user stack