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References: <20190515192715.18000-1-vgoyal@redhat.com>
 <20190515192715.18000-27-vgoyal@redhat.com>
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From: Eric Ren <ericdotren@gmail.com>
Date: Sun, 19 May 2019 15:48:05 +0800
Message-ID: <CAN+Pk99SNKSf+GjSQUUWt_eu1fSjTy_ByUOEQUXHi8zNqXY1zA@mail.gmail.com>
Subject: Re: [PATCH v2 26/30] fuse: Add logic to free up a memory range
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To: Vivek Goyal <vgoyal@redhat.com>
Cc: kvm@vger.kernel.org, miklos@szeredi.hu, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, dgilbert@redhat.com, stefanha@redhat.com, linux-fsdevel@vger.kernel.org, swhiteho@redhat.com
List-ID: <linux-nvdimm@lists.01.org>

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.

> +                       if (IS_ERR(alloc_dmap))
> +                               return PTR_ERR(alloc_dmap);
> +               }


Regards,
Eric
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