linux-kernel - Re: [PATCH 03/12] staging: lustre: llite: fix various issues with ll_splice

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Message-ID: <87o9shxcyq.fsf@notabene.neil.brown.name>
Date:   Wed, 19 Jul 2017 14:33:33 +1000
From:   NeilBrown <neilb@...e.com>
To:     Oleg Drokin <oleg.drokin@...el.com>,
        Al Viro <viro@...IV.linux.org.uk>
Cc:     Greg Kroah-Hartman <greg@...ah.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 03/12] staging: lustre: llite: fix various issues with ll_splice_alias.

On Tue, Jul 18 2017, Oleg Drokin wrote:

> Unfortunately this patch causes insta-crash on first stat call after mount.
> Sorry, I cannot dig into this deeper right this moment, but I will a bit later.

V.strange.  The crash suggests that the lock, and hence the inode, is
not initialized.  I cannot see how that might happen.
though...

>> +		spin_lock(&lli->lli_lock);
>> +		new = ll_find_invalid_alias(inode, de);
>> +		if (!new)
>> +			d_add(de, inode);
>> +		spin_lock(&lli->lli_lock);

Had it not crashed, it would have deadlocked.  That second spin_lock()
should be spin_unlock() :-( I don't *think* that would have caused this crash...

> I am adding Al that we discussed this code at some length and he found no problems
> here, so I am a bit surprised by your findings.

I'd be very happy to read Al's thoughts.

> Also the reason we reinvent the d_splice_alias is because we need to
> splice not just directories, but also regular files.

I see that.  A key simplification I bring is that directories and
non-directories can be handled separately.  d_splice_alias() does
all we need for directories, and nothing useful for non-dirs.

Thanks,
NeilBrown

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