Blackfin: make EVT3->EVT5 lowering more robust wrt IPEND[4]
We handle many exceptions at EVT5 (hardware error level) so that we can
catch exceptions in our exception handling code. Today - if the global
interrupt enable bit (IPEND[4]) is set (interrupts disabled) our trap
handling code goes into a infinite loop, since we need interrupts to be
on to defer things to EVT5.
Normal kernel code should not trigger this for any reason as IPEND[4] gets
cleared early (when doing an interrupt context save) and the kernel stack
there should be sane (or something much worse is happening in the system).
But there have been a few times where this has happened, so this change
makes sure we dump a proper crash message even when things have gone south.
Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/arch/blackfin/mach-common/entry.S b/arch/blackfin/mach-common/entry.S
index fb1795d..4c07fcb 100644
--- a/arch/blackfin/mach-common/entry.S
+++ b/arch/blackfin/mach-common/entry.S
@@ -301,25 +301,31 @@
nop;
ENTRY(_ex_trap_c)
+ /* The only thing that has been saved in this context is
+ * (R7:6,P5:4), ASTAT & SP - don't use anything else
+ */
+
+ GET_PDA(p5, r6);
+
/* Make sure we are not in a double fault */
p4.l = lo(IPEND);
p4.h = hi(IPEND);
r7 = [p4];
CC = BITTST (r7, 5);
if CC jump _double_fault;
+ [p5 + PDA_EXIPEND] = r7;
/* Call C code (trap_c) to handle the exception, which most
* likely involves sending a signal to the current process.
* To avoid double faults, lower our priority to IRQ5 first.
*/
- P5.h = _exception_to_level5;
- P5.l = _exception_to_level5;
+ r7.h = _exception_to_level5;
+ r7.l = _exception_to_level5;
p4.l = lo(EVT5);
p4.h = hi(EVT5);
- [p4] = p5;
+ [p4] = r7;
csync;
- GET_PDA(p5, r6);
#ifndef CONFIG_DEBUG_DOUBLEFAULT
/*
@@ -349,8 +355,7 @@
BITCLR(r6, SYSCFG_SSSTEP_P);
SYSCFG = r6;
- /* Disable all interrupts, but make sure level 5 is enabled so
- * we can switch to that level. Save the old mask. */
+ /* Save the current IMASK, since we change in order to jump to level 5 */
cli r6;
[p5 + PDA_EXIMASK] = r6;
@@ -358,9 +363,21 @@
p4.h = hi(SAFE_USER_INSTRUCTION);
retx = p4;
+ /* Disable all interrupts, but make sure level 5 is enabled so
+ * we can switch to that level.
+ */
r6 = 0x3f;
sti r6;
+ /* In case interrupts are disabled IPEND[4] (global interrupt disable bit)
+ * clear it (re-enabling interrupts again) by the special sequence of pushing
+ * RETI onto the stack. This way we can lower ourselves to IVG5 even if the
+ * exception was taken after the interrupt handler was called but before it
+ * got a chance to enable global interrupts itself.
+ */
+ [--sp] = reti;
+ sp += 4;
+
raise 5;
jump.s _bfin_return_from_exception;
ENDPROC(_ex_trap_c)
@@ -420,47 +437,52 @@
ENTRY(_exception_to_level5)
SAVE_ALL_SYS
- GET_PDA(p4, r7); /* Fetch current PDA */
- r6 = [p4 + PDA_RETX];
+ GET_PDA(p5, r7); /* Fetch current PDA */
+ r6 = [p5 + PDA_RETX];
[sp + PT_PC] = r6;
- r6 = [p4 + PDA_SYSCFG];
+ r6 = [p5 + PDA_SYSCFG];
[sp + PT_SYSCFG] = r6;
- /* Restore interrupt mask. We haven't pushed RETI, so this
- * doesn't enable interrupts until we return from this handler. */
- r6 = [p4 + PDA_EXIMASK];
- sti r6;
-
/* Restore the hardware error vector. */
- P5.h = _evt_ivhw;
- P5.l = _evt_ivhw;
+ r7.h = _evt_ivhw;
+ r7.l = _evt_ivhw;
p4.l = lo(EVT5);
p4.h = hi(EVT5);
- [p4] = p5;
+ [p4] = r7;
csync;
- p2.l = lo(IPEND);
- p2.h = hi(IPEND);
- csync;
- r0 = [p2]; /* Read current IPEND */
- [sp + PT_IPEND] = r0; /* Store IPEND */
+#ifdef CONFIG_DEBUG_DOUBLEFAULT
+ /* Now that we have the hardware error vector programmed properly
+ * we can re-enable interrupts (IPEND[4]), so if the _trap_c causes
+ * another hardware error, we can catch it (self-nesting).
+ */
+ [--sp] = reti;
+ sp += 4;
+#endif
+
+ r7 = [p5 + PDA_EXIPEND] /* Read the IPEND from the Exception state */
+ [sp + PT_IPEND] = r7; /* Store IPEND onto the stack */
r0 = sp; /* stack frame pt_regs pointer argument ==> r0 */
SP += -12;
call _trap_c;
SP += 12;
-#ifdef CONFIG_DEBUG_DOUBLEFAULT
- /* Grab ILAT */
- p2.l = lo(ILAT);
- p2.h = hi(ILAT);
- r0 = [p2];
- r1 = 0x20; /* Did I just cause anther HW error? */
- r0 = r0 & r1;
- CC = R0 == R1;
- if CC JUMP _double_fault;
-#endif
+ /* If interrupts were off during the exception (IPEND[4] = 1), turn them off
+ * before we return.
+ */
+ CC = BITTST(r7, EVT_IRPTEN_P)
+ if !CC jump 1f;
+ /* this will load a random value into the reti register - but that is OK,
+ * since we do restore it to the correct value in the 'RESTORE_ALL_SYS' macro
+ */
+ sp += -4;
+ reti = [sp++];
+1:
+ /* restore the interrupt mask (IMASK) */
+ r6 = [p5 + PDA_EXIMASK];
+ sti r6;
call _ret_from_exception;
RESTORE_ALL_SYS