[ 31/75] sparc64: Eliminate obsolete __handle_softirq() function

From: Greg KH
Date: Thu Apr 19 2012 - 17:35:07 EST

3.3-stable review patch. If anyone has any objections, please let me know.


From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

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@xxxxxxxx>
Suggested-by: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Tested-by: Meelis Roos <mroos@xxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/sparc/kernel/rtrap_64.S | 7 -------
1 file changed, 7 deletions(-)

--- a/arch/sparc/kernel/rtrap_64.S
+++ b/arch/sparc/kernel/rtrap_64.S
@@ -20,11 +20,6 @@

.align 32
- call do_softirq
- nop
- ba,a,pt %xcc, __handle_softirq_continue
- nop
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
sethi %hi(0xf << 20), %l4
and %l1, %l4, %l4

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