Commit b6835ea7 authored by Alexey Brodkin's avatar Alexey Brodkin Committed by Vineet Gupta


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

[1] 's avatarAlexey Brodkin <>
Cc: <> # 4.8+
Signed-off-by: 's avatarVineet Gupta <>
[vgupta: reworked changelog, added dependency on LL64+LLSC]
parent 493a2f81
......@@ -52,6 +52,17 @@
#define cache_line_size() 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)
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);
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment