ARC: define ARCH_SLAB_MINALIGN = 8
The default value of ARCH_SLAB_MINALIGN in "include/linux/slab.h" is
"__alignof__(unsigned long long)" which for ARC unexpectedly turns out
to be 4. This is not a compiler bug, but as defined by ARC ABI [1]
Thus slab allocator would allocate a struct which is 32-bit aligned,
which is generally OK even if struct has long long members.
There was however potetial problem when it had any atomic64_t which
use LLOCKD/SCONDD instructions which are required by ISA to take
64-bit addresses. This is the problem we ran into
[ 4.015732] EXT4-fs (mmcblk0p2): re-mounted. Opts: (null)
[ 4.167881] Misaligned Access
[ 4.172356] Path: /bin/busybox.nosuid
[ 4.176004] CPU: 2 PID: 171 Comm: rm Not tainted 4.19.14-yocto-standard #1
[ 4.182851]
[ 4.182851] [ECR ]: 0x000d0000 => Check Programmer's Manual
[ 4.190061] [EFA ]: 0xbeaec3fc
[ 4.190061] [BLINK ]: ext4_delete_entry+0x210/0x234
[ 4.190061] [ERET ]: ext4_delete_entry+0x13e/0x234
[ 4.202985] [STAT32]: 0x80080002 : IE K
[ 4.207236] BTA: 0x9009329c SP: 0xbe5b1ec4 FP: 0x00000000
[ 4.212790] LPS: 0x9074b118 LPE: 0x9074b120 LPC: 0x00000000
[ 4.218348] r00: 0x00000040 r01: 0x00000021 r02: 0x00000001
...
...
[ 4.270510] Stack Trace:
[ 4.274510] ext4_delete_entry+0x13e/0x234
[ 4.278695] ext4_rmdir+0xe0/0x238
[ 4.282187] vfs_rmdir+0x50/0xf0
[ 4.285492] do_rmdir+0x9e/0x154
[ 4.288802] EV_Trap+0x110/0x114
The fix is to make sure slab allocations are 64-bit aligned.
Do note that atomic64_t is __attribute__((aligned(8)) which means gcc
does generate 64-bit aligned references, relative to beginning of
container struct. However the issue is if the container itself is not
64-bit aligned, atomic64_t ends up unaligned which is what this patch
ensures.
[1] https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain/wiki/files/ARCv2_ABI.pdf
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: <stable@vger.kernel.org> # 4.8+
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: reworked changelog, added dependency on LL64+LLSC]
1 file changed
