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Subject[PATCH 4.20 154/183] ARC: define ARCH_SLAB_MINALIGN = 8
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Brodkin <abrodkin@synopsys.com>

commit b6835ea77729e7faf4656ca637ba53f42b8ee3fd upstream.

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]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arc/include/asm/cache.h | 11 +++++++++++
1 file changed, 11 insertions(+)

--- a/arch/arc/include/asm/cache.h
+++ b/arch/arc/include/asm/cache.h
@@ -52,6 +52,17 @@
#define cache_line_size() SMP_CACHE_BYTES
#define ARCH_DMA_MINALIGN SMP_CACHE_BYTES

+/*
+ * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses
+ * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit
+ * alignment for any atomic64_t embedded in buffer.
+ * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed
+ * value of 4 (and not 8) in ARC ABI.
+ */
+#if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC)
+#define ARCH_SLAB_MINALIGN 8
+#endif
+
extern void arc_cache_init(void);
extern char *arc_cache_mumbojumbo(int cpu_id, char *buf, int len);
extern void read_decode_cache_bcr(void);

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