Re: [PATCH -next] openrisc: Define __ro_after_init to avoid crash

From: Stafford Horne
Date: Tue Sep 27 2016 - 10:16:20 EST

On Sat, 24 Sep 2016, Guenter Roeck wrote:

openrisc qemu tests fail with the following crash.

Unable to handle kernel access at virtual address 0xc0300c34

Oops#: 0001
CPU #: 0
PC: c016c710 SR: 0000ae67 SP: c1017e04
GPR00: 00000000 GPR01: c1017e04 GPR02: c0300c34 GPR03: c0300c34
GPR04: 00000000 GPR05: c0300cb0 GPR06: c0300c34 GPR07: 000000ff
GPR08: c107f074 GPR09: c0199ef4 GPR10: c1016000 GPR11: 00000000
GPR12: 00000000 GPR13: c107f044 GPR14: c0473774 GPR15: 07ce0000
GPR16: 00000000 GPR17: c107ed8a GPR18: 00009600 GPR19: c107f044
GPR20: c107ee74 GPR21: 00000003 GPR22: c0473770 GPR23: 00000033
GPR24: 000000bf GPR25: 00000019 GPR26: c046400c GPR27: 00000001
GPR28: c0464028 GPR29: c1018000 GPR30: 00000006 GPR31: ccf37483
RES: 00000000 oGPR11: ffffffff
Process swapper (pid: 1, stackpage=c1001960)

Stack: Stack dump [0xc1017cf8]:
sp + 00: 0xc1017e04
sp + 04: 0xc0300c34
sp + 08: 0xc0300c34
sp + 12: 0x00000000

Bisect points to commit d2ec3f77de8e ("pty: make ptmx file ops read-only
after init"). Fix by defining __ro_after_init for the openrisc
architecture, similar to parisc.

Thanks for finding this one.
Just for clatify __read_mostly falls back to default blank in openrisc, so it gets no special section treatment.

Acked-by: Stafford Horne <shorne@xxxxxxxxx>

Fixes: d2ec3f77de8e ("pty: make ptmx file ops read-only after init")
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
arch/openrisc/include/asm/cache.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/openrisc/include/asm/cache.h b/arch/openrisc/include/asm/cache.h
index 4ce7a01a252d..5f55da9cbfd5 100644
--- a/arch/openrisc/include/asm/cache.h
+++ b/arch/openrisc/include/asm/cache.h
@@ -23,6 +23,8 @@
* they shouldn't be hard-coded!

+#define __ro_after_init __read_mostly
#define L1_CACHE_BYTES 16
#define L1_CACHE_SHIFT 4