Re: ZFS command can block the whole ZFS subsystem!

----- Original Message ----- 
From: "O. Hartmann" <ohartman_at_zedat.fu-berlin.de>
> 
> For some security reasons, I dumped via "dd" a large file onto a 3TB
> disk. The systems is 11.0-CURRENT #1 r259667: Fri Dec 20 22:43:56 CET
> 2013 amd64. Filesystem in question is a single ZFS pool.
> 
> Issuing the command
> 
> "rm dumpfile.txt"
> 
> and then hitting Ctrl-Z to bring the rm command into background via
> fg" (I use FreeBSD's csh in that console) locks up the entire command
> and even worse - it seems to wind up the pool in question for being
> exported!

I cant think of any reason why backgrounding a shell would export a pool.

> I expect to get the command into the background as every other UNIX
> command does when sending Ctrl-Z in the console. Obviously, ZFS
> related stuff in FreeBSD doesn't comply. 
> 
> The file has been removed from the pool but the console is still stuck
> with "^Z fg" (as I typed this in). Process list tells me:
> 
> top
> 17790 root             1  20    0  8228K  1788K STOP   10   0:05
> 0.00% rm
> 
> for the particular "rm" command issued.

Thats not backgrounded yet otherwise it wouldnt be in the state STOP.

> Now, having the file deleted, I'd like to export the pool for further
> maintainance

Are you sure the delete is complete? Also don't forget ZFS has TRIM by
default, so depending on support of the underlying devices you could
be seeing deletes occuring.

You can check that gstat -d

> but that doesn't work with
> 
> zpool export -f poolname
> 
> This command is now also stuck blocking the terminal and the pool from
> further actions.

If the delete hasnt completed and is stuck in the kernel this is
to be expected.
> 
> This is painful. Last time I faced the problem, I had to reboot prior
> to take any action regarding any pool in the system, since one single
> ZFS command could obviously block the whole subsystem (I tried to
> export and import).
> 
> What is up here?

    Regards
    Steve

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