ZFS/GFS locking fixes

[Will Andrews]

Hi,

I’ve been on vacation for the last 2 weeks.  I’ll take a look at it today, work on merging your changes with mine, and then port them forward to FreeBSD/head.

Thanks for the report and your patch.

—Will.

From: krichy at cflinux.hu krichy at cflinux.hu
Reply: krichy at cflinux.hu krichy at cflinux.hu
Date: January 2, 2014 at 3:22:48 AM
To: Richard Kojedzinszky krichy at cflinux.hu
Subject:  Re: ZFS/GFS locking fixes  
Dear list,

Is there any progress regarding my issues/patches?

Thanks,
2013-12-29 23:45 időpontban Richard Kojedzinszky ezt írta:
> Dear devs,
>  
> Maybe PJD has forwarded my conversation with him, I've made to fixes
> for my zfs/gfs locking issues. They can be found here:
> https://github.com/rkojedzinszky/freebsd/commits/releng/9.2-zfs
>  
> While this solves most of my discovered issues, one still remained.
> Commit
> https://github.com/rkojedzinszky/freebsd/commit/1d8972b3f353f986eb5b85bc108b1c0d946d3218
> introduced another deadlock possibility:
> When 'zfs send -R' tries to exit, it calls zfsdev_close(), which
> acquires spa_namespace_lock, which then invokes zfs_unmount_snap(),
> which goes to
> zfsctl_snapshot_inactive() which will lock the .zfs/snapshot's
> sdp->sd_lock. The same time, when zfsctl_snapdir_lookup() is running,
> holding the same directory's sdp->sd_lock, tries to mount a snapshot,
> which somewhere tries to acquire spa_namespace_lock, and they got into
> a deadlock.
>  
> This problem also can be used to DoS a system, as an administrator may
> have set up to backup its system using zfs send, and a normal user can
> initiate the other process (the mount).
>  
> What could be the solution?
>  
> Thanks in advance,
> Kojedzinszky Richard
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Will Andrews
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