linux-kernel - Re: [PATCH v2 26/30] fuse: Add logic to free up a memory range

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Message-ID: <20190520125355.GA28008@redhat.com>
Date:   Mon, 20 May 2019 08:53:55 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Eric Ren <ericdotren@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-nvdimm@...ts.01.org, miklos@...redi.hu,
        stefanha@...hat.com, dgilbert@...hat.com, swhiteho@...hat.com
Subject: Re: [PATCH v2 26/30] fuse: Add logic to free up a memory range

On Sun, May 19, 2019 at 03:48:05PM +0800, Eric Ren wrote:
> Hi,
> 
> @@ -1784,8 +1822,23 @@ static int fuse_iomap_begin(struct inode *inode,
> > loff_t pos, loff_t length,
> >                 if (pos >= i_size_read(inode))
> >                         goto iomap_hole;
> >
> > -               alloc_dmap = alloc_dax_mapping(fc);
> > -               if (!alloc_dmap)
> > +               /* Can't do reclaim in fault path yet due to lock ordering.
> > +                * Read path takes shared inode lock and that's not
> > sufficient
> > +                * for inline range reclaim. Caller needs to drop lock,
> > wait
> > +                * and retry.
> > +                */
> > +               if (flags & IOMAP_FAULT || !(flags & IOMAP_WRITE)) {
> > +                       alloc_dmap = alloc_dax_mapping(fc);
> > +                       if (!alloc_dmap)
> > +                               return -ENOSPC;
> > +               } else {
> > +                       alloc_dmap = alloc_dax_mapping_reclaim(fc, inode);
> >
> 
> alloc_dmap could be NULL as follows:
> 
> alloc_dax_mapping_reclaim
>    -->fuse_dax_reclaim_first_mapping
>              -->fuse_dax_reclaim_first_mapping_locked
>                   --> fuse_dax_interval_tree_iter_first  ==> return NULL
> and
> 
> IS_ERR(NULL) is false, so we may miss that error case.

Hi Eric,

Good catch. I will fix it next version. 

Thanks
Vivek