btrfs filesystem defrag fails with "Resource temporarily unavailable" when strace'd
I started...
btrfs filesystem defragment -v /some/directory
and this took (unexpectedly, for just 150M of data) a long time (minutes).
So I wondered whether I could see via "strace -p PID" what was going on with the process.
Immediately when strace tries to attach, the btrfs process dies with this error message:
Quoted 1 line
ERROR: defrag failed on /some/directory - Resource temporarily unavailable
This is 100% reproducable.
The strace output looks like this:
Quoted 11 lines
Process 1402 attached
brk(0) = 0x1468000 brk(0) = 0x1468000 brk(0x1460000) = 0x1460000 brk(0) = 0x1460000 close(3) = 0 write(2, "ERROR: defrag failed on /some/d"..., 84) = 84 write(1, "btrfs-progs v4.1\n", 17) = 17 write(2, "total 1 failures\n", 17) = 17 exit_group(1) = ?+++ exited with 1 +++
This is the first time I see a prozess crash upon strace being attached - is this intended behaviour? If so... why?
(Tried again without strace, "the btrfs filesystem defragment" command later finished ok, albeight after a loong time.)
Regards,
Lutz Vieweg