I'm rather suspicious of r292255 here -- royger, hps, kib, can any of you
comment on whether it would be responsible for making non-page-aligned I/Os
no longer get split on page boundaries?  The commit message is suggestive,
but I don't know the code very well.

(If I don't hear back I'll determine if it's responsible experimentally, but
testing a "system no longer boots" bug in EC2 is painfully slow and it's
getting late here.)

Colin Percival

On 01/10/16 22:28, Colin Percival wrote:
> Some time in early December, disk I/O broke.  The EC2 image built from r291495
> works fine; the EC2 image built from r292413 is broken.
> 
> Symptoms:
> 1. growfs reports "superblock not recognized"
> 
> 2. fsck reports lots of "UNKNOWN FILE TYPE"s and after a few seconds provokes
> "panic: XEN disk driver data cannot cross a page boundary"
> xbd_mksegarray() at xbd_mksegarray+0x4b/frame 0xfffffe0f4dadb420
> 
> xbd_queue_cb() at xbd_queue_cb+0x1e8/frame 0xfffffe0f4dadb490
> 
> bus_dmamap_load_bio() at bus_dmamap_load_bio+0xad/frame 0xfffffe0f4dadb4f0
> 
> xbd_startio() at xbd_startio+0x194/frame 0xfffffe0f4dadb530
> 
> xbd_strategy() at xbd_strategy+0x6a/frame 0xfffffe0f4dadb560
> 
> g_disk_start() at g_disk_start+0x37c/frame 0xfffffe0f4dadb5d0
> 
> g_io_request() at g_io_request+0x39d/frame 0xfffffe0f4dadb630
> 
> g_part_start() at g_part_start+0x2b5/frame 0xfffffe0f4dadb6b0
> 
> g_io_request() at g_io_request+0x39d/frame 0xfffffe0f4dadb710
> 
> g_io_request() at g_io_request+0x39d/frame 0xfffffe0f4dadb770
> 
> g_dev_strategy() at g_dev_strategy+0x171/frame 0xfffffe0f4dadb7b0
> 
> physio() at physio+0x440/frame 0xfffffe0f4dadb850
> 
> devfs_read_f() at devfs_read_f+0xe7/frame 0xfffffe0f4dadb8b0
> 
> dofileread() at dofileread+0x98/frame 0xfffffe0f4dadb900
> 
> kern_readv() at kern_readv+0x68/frame 0xfffffe0f4dadb950
> 
> sys_read() at sys_read+0x60/frame 0xfffffe0f4dadb9a0
> 
> 
> Does anyone remember touching any relevant bits of code in that timeframe?
> 

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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