4.20-stable review patch. If anyone has any objections, please let me know.
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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...
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);