Hi,All.
Today I have upgraded the kernel version from 3.17.4 to 3.19.3 (APM aarch64), found some strange error , and these error caused the system can not enter the command,I picked up the main error : 


[   43.055594] ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[   43.062618] ata2.00: failed command: READ DMA EXT
[   43.067316] ata2.00: cmd 25/00:08:e0:76:df/00:00:e5:00:00/e0 tag 0 dma 4096 in
[   43.067316]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[   43.081865] ata2.00: status: { DRDY }
[   43.085514] ata2: hard resetting link
[   43.435577] ata2: SATA link up 6.0 Gbps (SStatus 133 SControl 4300)
[   43.442510] ata2.00: configured for UDMA/133
[   43.446775] ata2.00: device reported invalid CHS sector 0
[   43.452156] ata2: EH complete

Here are some dmesg output : 

[    0.013618] WARNING: CPU: 0 PID: 1 at drivers/firmware/dmi_scan.c:657 dmi_matches+0x10c/0x110()
[    0.013623] dmi check: not initialized yet.
[    0.013626] Modules linked in:
[    0.013632] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.19.3-200.fc21.aarch64 #1
[    0.013636] Hardware name: APM X-Gene Mustang board (DT)
[    0.013640] Call trace:
[    0.013646] [<fffffe0000097624>] dump_backtrace+0x0/0x164
[    0.013651] [<fffffe00000977a4>] show_stack+0x1c/0x28
[    0.013657] [<fffffe000077fd88>] dump_stack+0x74/0x94
[    0.013662] [<fffffe00000bd908>] warn_slowpath_common+0xa4/0xdc
[    0.013667] [<fffffe00000bd9b4>] warn_slowpath_fmt+0x74/0x88
[    0.013671] [<fffffe00005f9b80>] dmi_matches+0x108/0x110
[    0.013676] [<fffffe00005f9bb4>] dmi_check_system+0x2c/0x70
[    0.013681] [<fffffe0000c6e614>] lockup_detector_init+0x10/0x54
[    0.013685] [<fffffe0000c60acc>] kernel_init_freeable+0x108/0x260
[    0.013690] [<fffffe000077d7b4>] kernel_init+0x1c/0xe0
[    0.013705] ---[ end trace f44b0c4387855b6d ]---
[    0.013708] ------------[ cut here ]------------
[    0.013713] WARNING: CPU: 0 PID: 1 at drivers/firmware/dmi_scan.c:657 dmi_matches+0x10c/0x110()
[    0.013718] dmi check: not initialized yet.
[    0.013721] Modules linked in:
[    0.013725] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W      3.19.3-200.fc21.aarch64 #1
[    0.013730] Hardware name: APM X-Gene Mustang board (DT)
[    0.013733] Call trace:
[    0.013737] [<fffffe0000097624>] dump_backtrace+0x0/0x164
[    0.013741] [<fffffe00000977a4>] show_stack+0x1c/0x28
[    0.013745] [<fffffe000077fd88>] dump_stack+0x74/0x94
[    0.013750] [<fffffe00000bd908>] warn_slowpath_common+0xa4/0xdc
[    0.013754] [<fffffe00000bd9b4>] warn_slowpath_fmt+0x74/0x88
[    0.013759] [<fffffe00005f9b80>] dmi_matches+0x108/0x110
[    0.013763] [<fffffe00005f9bb4>] dmi_check_system+0x2c/0x70
[    0.013767] [<fffffe0000c6e614>] lockup_detector_init+0x10/0x54
[    0.013772] [<fffffe0000c60acc>] kernel_init_freeable+0x108/0x260
[    0.013776] [<fffffe000077d7b4>] kernel_init+0x1c/0xe0
[    0.013780] ---[ end trace f44b0c4387855b6e ]—

How to fix it??
Thanks very much!