msync stalls with current master (cda4db408...)

[r0ssar00]

Background+history: I've been using the launchpad ubuntu dailies on precise for a couple of months and the latest update introduced a regression in the initrd generation so I reverted back to an older version of the initrd support for zfs and then grabbed cda4db4 and openzfs/spl@dd87332 and built+installed both.

Since this update, every time I attempt to run a command that attempts an msync on my zfs rootfs, the msync call stalls and leaves the system's I/O wait maxed out ("wa" in top, not sure if I've used the proper phrasing+terminology here but I hope the idea is at least there). I ran an apt-get update using strace and the last few lines are

read(6, "aspell-mr (<= 0.10-1)\nProvides: "..., 65262) = 65262
read(6, " mutiple instances over DBus - s"..., 65200) = 65200
read(6, "ation on a large\n network, or a "..., 64105) = 43090
read(6, "", 21015)                      = 0
close(6)                                = 0
msync(0x7f8e4c638000, 53490348, MS_SYNC

The missing ')' after MS_SYNC is intentional.

It seems a deadlock has been introduced between the daily v0.6.0.75 (0ef0ff5) and master.

[dechamps]

You're saying that the call stalls indefinitely, right? It doesn't complete after 5 seconds or so?

Can you try reverting 2b28613 and see how it goes? Also, it would be interesting to test with my msync.c program described in #907.

[r0ssar00]

Exactly. I sat there for a half hour or so waiting for it to complete with no progress.

Will do, however it may be a few days until I can actually try this due to school.

[behlendorf]

Yes, please try reverting 2b28613 . If you could also collect the stack tracks from the system when it's hung that would be helpful. As root just echo t >proc/sysrq-trigger and then grab them from dmesg.

[behlendorf]

This was resolved by commit 8312c6d

[r0ssar00]

After testing a few days using current HEAD, it seems 8312c6d is the solution. At first, I got hundreds of exceptions in one of the spl threads (the log files actually exhausted disk space before I realized) but those resolved themselves too.