linux-kernel - Re: [PATCH] writeback: safer lock nesting

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Date:   Fri, 06 Apr 2018 18:49:35 +0000
From:   Greg Thelen <gthelen@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wang Long <wanglong19@...tuan.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, npiggin@...il.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH] writeback: safer lock nesting

On Fri, Apr 6, 2018 at 1:07 AM Michal Hocko <mhocko@...nel.org> wrote:

> On Fri 06-04-18 01:03:24, Greg Thelen wrote:
> [...]
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index d4d04fee568a..d51bae5a53e2 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -746,10 +746,11 @@ int inode_congested(struct inode *inode, int
cong_bits)
> >       if (inode && inode_to_wb_is_valid(inode)) {
> >               struct bdi_writeback *wb;
> >               bool locked, congested;
> > +             unsigned long flags;
> >
> > -             wb = unlocked_inode_to_wb_begin(inode, &locked);
> > +             wb = unlocked_inode_to_wb_begin(inode, &locked, &flags);

> Wouldn't it be better to have a cookie (struct) rather than 2 parameters
> and let unlocked_inode_to_wb_end DTRT?

Nod.  I'll post a V2 patch with that change.

> >               congested = wb_congested(wb, cong_bits);
> > -             unlocked_inode_to_wb_end(inode, locked);
> > +             unlocked_inode_to_wb_end(inode, locked, flags);
> >               return congested;
> >       }
> --
> Michal Hocko
> SUSE Labs