From: Al Viro <viro@ZenIV.linux.org.uk>
To: Chris Mason <clm@fb.com>, Marc MERLIN <marc@merlins.org>,
linux-btrfs@vger.kernel.org
Subject: Re: Can you help explain these OOM crashes?
Date: Fri, 26 Feb 2016 02:05:19 +0000 [thread overview]
Message-ID: <20160226020519.GZ17997@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20160225194251.kidqfejwlsai6h5v@floor.thefacebook.com>
On Thu, Feb 25, 2016 at 02:42:51PM -0500, Chris Mason wrote:
> Al, any ideas why get_anon_bdev is doing an atomic allocation here?
>
> if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
Because set() callback of sget() runs under sb_lock - it must be atomic
wrt scanning the list of superblock in search of match. And get_anon_bdev()
is called from such callbacks...
In principle, we could change locking rules for case when test callback
is NULL, except that it's also called from ns_set_super(), which *does*
come along with non-NULL test() (see mount_ns()), so that really doesn't
help...
prev parent reply other threads:[~2016-02-26 2:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-25 19:20 Can you help explain these OOM crashes? Marc MERLIN
2016-02-25 19:42 ` Chris Mason
2016-02-26 2:05 ` Al Viro [this message]
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