[PATCH] sparc32: keep PIL raised on the SMP ticker and LEON IPI exit paths

[Imre Kaloz <kaloz@kernel.org>]

smp4m_ticker returns from smp4m_percpu_timer_interrupt() by writing the
interrupted %psr back with traps enabled, which drops PIL before
RESTORE_ALL. A level 14 tick pending again at that point is taken on
top of the current trap frame, so back-to-back ticks nest one frame per
tick until the 8K kernel stack runs into thread_info. Keep PIL at 15
until rett restores the interrupted %psr, as real_irq_continue does.

smp4d_ticker and smpleon_ipi exit the same way and get the same change.

Broken since 2.1.36 (sun4m), 2.1.97 (sun4d) and 2.6.33 (LEON).

Cc: stable@vger.kernel.org
Signed-off-by: Imre Kaloz <kaloz@kernel.org>
---

Notes:
    No Fixes: tag: this has been broken since 2.1.36 on sun4m (as
    smp_ticker) and since 2.1.97 on sun4d, before the git history. The
    LEON exit came with smpleon_ticker in 8401707ff645 ("sparc,leon:
    Sparc-Leon SMP support") in 2.6.33 and moved to smpleon_ipi in 3.0; a
    Fixes: tag naming one commit would date all three sites to it.

 arch/sparc/kernel/entry.S | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/sparc/kernel/entry.S b/arch/sparc/kernel/entry.S
index ea51ef52c952..7288da5f6727 100644
--- a/arch/sparc/kernel/entry.S
+++ b/arch/sparc/kernel/entry.S
@@ -252,7 +252,8 @@ smp4m_ticker:
 	WRITE_PAUSE
 	call	smp4m_percpu_timer_interrupt
 	 add	%sp, STACKFRAME_SZ, %o0
-	wr	%l0, PSR_ET, %psr
+	or	%l0, PSR_PIL, %g2	! keep PIL raised until rett, or a
+	wr	%g2, PSR_ET, %psr	! re-asserted tick nests on this frame
 	WRITE_PAUSE
 	RESTORE_ALL
 
@@ -353,7 +354,8 @@ smp4d_ticker:
 	WRITE_PAUSE
 	call	smp4d_percpu_timer_interrupt
 	 add	%sp, STACKFRAME_SZ, %o0
-	wr	%l0, PSR_ET, %psr
+	or	%l0, PSR_PIL, %g2	! keep PIL raised until rett, or a
+	wr	%g2, PSR_ET, %psr	! re-asserted tick nests on this frame
 	WRITE_PAUSE
 	RESTORE_ALL
 
@@ -407,7 +409,8 @@ smpleon_ipi:
 	WRITE_PAUSE
 	call	leonsmp_ipi_interrupt
 	 add	%sp, STACKFRAME_SZ, %o1 ! pt_regs
-	wr	%l0, PSR_ET, %psr
+	or	%l0, PSR_PIL, %g2	! keep PIL raised until rett, or a
+	wr	%g2, PSR_ET, %psr	! re-asserted IPI nests on this frame
 	WRITE_PAUSE
 	RESTORE_ALL
 

base-commit: 62f4c998b297cf233997a2b4cd6fc2d2df0319c9
-- 
2.47.3