From: Viacheslav Dubeyko <slava@dubeyko.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: "Ernesto A. Fernández" <ernesto.mnd.fernandez@gmail.com>,
linux-fsdevel@vger.kernel.org,
"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/2] hfsplus: update timestamps on truncate()
Date: Tue, 16 Oct 2018 19:01:21 -0700 [thread overview]
Message-ID: <1539741681.3153.5.camel@slavad-ubuntu-14.04> (raw)
In-Reply-To: <20181015212416.GY32577@ZenIV.linux.org.uk>
On Mon, 2018-10-15 at 22:24 +0100, Al Viro wrote:
> On Mon, Oct 15, 2018 at 02:02:01PM -0700, Viacheslav Dubeyko wrote:
> > > 1) unlink() finds the victim and locks it
> > >
> > > 2) in hfsplus_file_release():
> > > if (atomic_dec_and_test(&HFSPLUS_I(inode)->opencnt)) {
> > > got to 0
> > > inode_lock(inode);
> > > block waiting for unlink
> > >
> > > 3) open() finds the sucker in dcache and hits hfsplus_file_open(), where
> > > we do
> > > atomic_inc(&HFSPLUS_I(inode)->opencnt);
> > > and now opencnt is 1.
> > >
> > > 4) on the unlink side:
> > > if (inode->i_ino == cnid &&
> > > atomic_read(&HFSPLUS_I(inode)->opencnt)) {
> > > str.name = name;
> > > str.len = sprintf(name, "temp%lu", inode->i_ino);
> > > res = hfsplus_rename_cat(inode->i_ino,
> > > dir, &dentry->d_name,
> > > sbi->hidden_dir, &str);
> > > if (!res) {
> > > inode->i_flags |= S_DEAD;
> > > drop_nlink(inode);
> > > }
> > > goto out;
> > > }
> > > nlink is zero now, the sucker got renamed and marked S_DEAD
> > >
> > > 5) ->release() finally got through inode_lock() and
> > > hfsplus_file_truncate(inode);
> > > if (inode->i_flags & S_DEAD) {
> > > hfsplus_delete_cat(inode->i_ino,
> > > HFSPLUS_SB(sb)->hidden_dir, NULL);
> > > hfsplus_delete_inode(inode);
> > > }
> > > inode_unlock(inode);
> > > ... and now we have killed everything we used to have associated with that
> > > inode on disk. While it's still open. What's to stop CNID to be reused,
> > > etc. and what's to preserve sanity in that situation?
> > >
> > > What am I missing there?
> >
> > OK. If you believe that the patch is in the bad shape then what's your
> > suggestion for improving the patch?
>
> Tha patch is OK; the problem, AFAICS, is neither introduced nor fixed by it.
> I might be wrong regarding the locking problem I described, but it does
> appear to be real and I'd like somebody more familiar with HFS+ to comment
> on it.
Yes, it looks like a mess. Let me take a deeper look in the code.
Thanks,
Vyacheslav Dubeyko.
next prev parent reply other threads:[~2018-10-17 9:54 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-12 4:22 [PATCH 1/2] hfsplus: update timestamps on truncate() Ernesto A. Fernández
2018-10-12 4:23 ` [PATCH 2/2] hfs: update timestamp " Ernesto A. Fernández
2018-10-12 21:57 ` Viacheslav Dubeyko
2018-10-12 21:57 ` [PATCH 1/2] hfsplus: update timestamps " Viacheslav Dubeyko
2018-10-13 2:42 ` Al Viro
2018-10-15 21:02 ` Viacheslav Dubeyko
2018-10-15 21:24 ` Al Viro
2018-10-17 2:01 ` Viacheslav Dubeyko [this message]
2018-10-18 2:09 ` Viacheslav Dubeyko
2018-10-16 23:15 ` Ernesto A. Fernández
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