linux-kernel - Re: [PATCH 2/2] jffs2: Provide jffs2_sync files to track gc POLL progress

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Message-ID: <CAFLxGvyTmz8JQVn-OJFSVdns74o49XgdWbhGpPsqYe5S2uahYg@mail.gmail.com>
Date:   Sun, 22 Jul 2018 15:17:07 +0200
From:   Richard Weinberger <richard.weinberger@...il.com>
To:     Theuns Verwoerd <Theuns.Verwoerd@...iedtelesis.co.nz>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 2/2] jffs2: Provide jffs2_sync files to track gc POLL progress

[fixing CC list]

On Fri, Jul 20, 2018 at 2:54 AM, Theuns Verwoerd
<Theuns.Verwoerd@...iedtelesis.co.nz> wrote:
>
> On 07/20/2018 12:04 PM, Al Viro wrote:
>> On Fri, Jul 20, 2018 at 11:50:12AM +1200, Theuns Verwoerd wrote:
>>
>>> +ssize_t jffs2_sync_file_read(struct file *f,
>>> +          char __user *b, size_t len, loff_t *ofs)
>>> +{
>>> +    struct jffs2_sb_info *c = file_inode(f)->i_private;
>>> +
>>> +    while (c->tidemark)
>>> +            schedule();
>>> +
>>> +    return 0;
>>> +}
>> Brilliant.  So when that gets called with c->tidemark being true and
>> need_resched() - false, we shall...
> By my reading, schedule() will happily force a reschedule (once) when
> need_resched() is false.  Every time the process is granted a time
> slice, it'll check the condition and surrender if not ready.
>
> What do you believe will happen?
>> Bonus question: what happens if that is called after that jffs2_sb_info
>> gets freed?
> That is probably a valid critique - if jffs2_kill_sb() gets called the
> cleanup in exit_jffs2_fs() is not sufficient.

Beside of that, IMHO this debugfs file is a gross hack.
Did you look into the possibility to add the GC phase into the unlink code?

-- 
Thanks,
//richard