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Date:      Wed, 17 Jul 2013 14:26:12 +0300
From:      Andriy Gapon <avg@FreeBSD.org>
To:        Adrian Chadd <adrian@FreeBSD.org>
Cc:        freebsd-fs@FreeBSD.org, freebsd-current <freebsd-current@FreeBSD.org>
Subject:   Re: Deadlock in nullfs/zfs somewhere
Message-ID:  <51E67F54.9080800@FreeBSD.org>
In-Reply-To: <CAJ-VmokR8jJpdRc_kBJzhW4_R1pJnj3UPfsG5ANpq-kEGwCP9g@mail.gmail.com>
References:  <CAJ-Vmomy3MrkSwJLQUGnDuD3EC3HzrudEghSDMeDwzVdaFNpLg@mail.gmail.com> <51DCFEDA.1090901@FreeBSD.org> <CAJ-VmokctCmV4%2By17uvqO9wXEyh0s%2BaXZ9nggvoAgP5%2BZHSgFA@mail.gmail.com> <51E59FD9.4020103@FreeBSD.org> <CAJ-VmokR8jJpdRc_kBJzhW4_R1pJnj3UPfsG5ANpq-kEGwCP9g@mail.gmail.com>

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on 16/07/2013 22:40 Adrian Chadd said the following:
> :(  So it's a deadlock. Ok, so what's next?

A creative process...

One possibility is to add getnewvnode_reserve() calls before the ZFS transaction
beginnings in the places where a new vnode/znode may have to be allocated within
a transaction.
This looks like a quick and cheap solution but it makes the code somewhat messier.

Another possibility is to change something in VFS machinery, so that VOP_RECLAIM
getting blocked for one filesystem does not prevent vnode allocation for other
filesystems.

I could think of other possible solutions via infrastructural changes in VFS or
ZFS...

-- 
Andriy Gapon



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