sparc64: Eliminate obsolete __handle_softirq() function

BugLink: http://bugs.launchpad.net/bugs/987283

commit 3d3eeb2ef26112a200785e5fca58ec58dd33bf1e upstream.

The invocation of softirq is now handled by irq_exit(), so there is no
need for sparc64 to invoke it on the trap-return path.  In fact, doing so
is a bug because if the trap occurred in the idle loop, this invocation
can result in lockdep-RCU failures.  The problem is that RCU ignores idle
CPUs, and the sparc64 trap-return path to the softirq handlers fails to
tell RCU that the CPU must be considered non-idle while those handlers
are executing.  This means that RCU is ignoring any RCU read-side critical
sections in those handlers, which in turn means that RCU-protected data
can be yanked out from under those read-side critical sections.

The shiny new lockdep-RCU ability to detect RCU read-side critical sections
that RCU is ignoring located this problem.

The fix is straightforward: Make sparc64 stop manually invoking the
softirq handlers.

Reported-by: Meelis Roos <mroos@linux.ee>
Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

1 files changed, 0 insertions, 7 deletions

diff --git a/arch/sparc/kernel/rtrap_64.S b/arch/sparc/kernel/rtrap_64.S
index 77f1b95e080..9171fc238de 100644
--- a/arch/sparc/kernel/rtrap_64.S
+++ b/arch/sparc/kernel/rtrap_64.S
@@ -20,11 +20,6 @@
 
                 .text
                 .align                  32
-__handle_softirq:
-                call                    do_softirq
-                 nop
-                ba,a,pt                 %xcc, __handle_softirq_continue
-                 nop
 __handle_preemption:
                 call                    schedule
                  wrpr                   %g0, RTRAP_PSTATE, %pstate
@@ -89,9 +84,7 @@ rtrap:
                 cmp                     %l1, 0
 
                 /* mm/ultra.S:xcall_report_regs KNOWS about this load. */
-                bne,pn                  %icc, __handle_softirq
                  ldx                    [%sp + PTREGS_OFF + PT_V9_TSTATE], %l1
-__handle_softirq_continue:
 rtrap_xcall:
                 sethi                   %hi(0xf << 20), %l4
                 and                     %l1, %l4, %l4