| Message ID | 20191030102810.20744-1-vincent.whitchurch@axis.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | buffer: Work around I/O errors due to ARM CPU bug | expand |
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h index 7b73ef7f902d..4ef909a91f8c 100644 --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -352,6 +352,14 @@ static inline void wait_on_buffer(struct buffer_head *bh) might_sleep(); if (buffer_locked(bh)) __wait_on_buffer(bh); + +#ifdef CONFIG_ARM + /* + * Work around ARM Cortex-A9 MPcore Read-after-Read Hazards (erratum + * 761319). + */ + smp_rmb(); +#endif } static inline int trylock_buffer(struct buffer_head *bh)
On my dual-core ARM Cortex-A9, reading from squashfs (over dm-verity/ubi/mtd) in a loop for hundreds of hours inevitably results in a read failure in squashfs_read_data(). The errors occur because the buffer_uptodate() check fails after wait_on_buffer(). Further debugging shows that the bh was in fact uptodate and that there is no actual I/O error in the lower layers. The problem appears to be caused by the read-after-read hazards in the ARM Cortex-A9 MPCore (erratum #761319, see [1]). The new value of the BH_Lock flag is seen but the new value of BH_Uptodate is not even though both the bits are read from the same memory location. Work around it by adding a DMB between the two reads of bh->flags. 27c: 9d08 ldr r5, [sp, #32] 27e: 2400 movs r4, #0 280: e006 b.n 290 <squashfs_read_data+0x290> 282: 6803 ldr r3, [r0, #0] 284: 07da lsls r2, r3, #31 286: f140 810d bpl.w 4a4 <squashfs_read_data+0x4a4> 28a: 3401 adds r4, #1 28c: 42bc cmp r4, r7 28e: da08 bge.n 2a2 <squashfs_read_data+0x2a2> 290: f855 0f04 ldr.w r0, [r5, #4]! 294: 6803 ldr r3, [r0, #0] 296: 0759 lsls r1, r3, #29 298: d5f3 bpl.n 282 <squashfs_read_data+0x282> 29a: f7ff fffe bl 0 <__wait_on_buffer> With this barrier, no failures have been seen in 2500+ hours of the same test. [1] http://infocenter.arm.com/help/topic/com.arm.doc.uan0004a/UAN0004A_a9_read_read.pdf Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> --- include/linux/buffer_head.h | 8 ++++++++ 1 file changed, 8 insertions(+)