[PATCH RFC v1] m68k: kernel/traps.c - only force 030 bus error if PC not in exception table

[Michael Schmitz <schmitzmic@gmail.com>]

__get_kernel_nofault() does copy data in supervisor mode when
forcing a task backtrace dump through the sysrq trigger.

Our 030 bus error handler is ill equipped to deal with this:

Whenever ssw indicates a kernel mode access on a data fault,
we don't even attempt to handle the fault and instead send
a bus error signal (or panic). As a result, the check for
exception handling at the fault PC (buried in send_sig_fault()
which gets called from do_page_fault() eventually) is never
used.

Both 040 and 060 access error handlers do not care whether
a fault happened on supervisor mode access, and will call
do_page_fault() even on those.

Add a check in bus_error030 to call do_page_fault() in case
we do have an entry for the fault PC in our exception table.

Tested on 030 Atari Falcon.

Signed-off-by: Michael Schmitz <schmitzmic@gmail.com># Please enter the commit message for your changes. Lines starting
CC: Eero Tamminen <oak@helsinkinet.fi>
CC: Finn Thain <ftain@linux-m68k.org>
CC: Andreas Schwab <schwab@linux-m68k.org>
CC: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/daca2f68-19fa-a2b6-97c6-16b5b7e26afe@helsinkinet.fi
---
 arch/m68k/kernel/traps.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index 5c8cba0efc63..67576fb0c466 100644
--- a/arch/m68k/kernel/traps.c
+++ b/arch/m68k/kernel/traps.c
@@ -30,6 +30,7 @@
 #include <linux/init.h>
 #include <linux/ptrace.h>
 #include <linux/kallsyms.h>
+#include <linux/extable.h>
 
 #include <asm/setup.h>
 #include <asm/fpu.h>
@@ -545,7 +546,7 @@ static inline void bus_error030 (struct frame *fp)
 			errorcode |= 2;
 
 		if (mmusr & (MMU_I | MMU_WP)) {
-			if (ssw & 4) {
+			if (ssw & 4 && !search_exception_tables(fp->ptregs.pc)) {
 				pr_err("Data %s fault at %#010lx in %s (pc=%#lx)\n",
 				       ssw & RW ? "read" : "write",
 				       fp->un.fmtb.daddr,
-- 
2.17.1