[PATCH v2] erofs: fix .fadvise() for page cache sharing

[Lihongbo(hb-lee,OS Lab)]

Ok, look good to me

Reviewed-by: Hongbo Li <lihongbo22 at huawei.com<mailto:lihongbo22 at huawei.com>>

Thanks.


________________________________
Li Hongbo
Mail: lihongbo22 at huawei.com<mailto:lihongbo22 at huawei.com>
发件人：Gao Xiang <hsiangkao at linux.alibaba.com<mailto:hsiangkao at linux.alibaba.com>>
收件人：linux-erofs at lists.ozlabs.org <linux-erofs at lists.ozlabs.org<mailto:linux-erofs at lists.ozlabs.org>>
抄 送：LKML <linux-kernel at vger.kernel.org<mailto:linux-kernel at vger.kernel.org>>; Gao Xiang <hsiangkao at linux.alibaba.com<mailto:hsiangkao at linux.alibaba.com>>; Lihongbo(hb-lee,OS Lab) <lihongbo22 at huawei.com<mailto:lihongbo22 at huawei.com>>
主 题：[PATCH v2] erofs: fix .fadvise() for page cache sharing
时 间：2026-03-24　23:54:15

Currently, .fadvise() doesn't work well if page cache sharing is on
since shared inodes belong to a pseudo fs generated with init_pseudo(),
and sb->s_bdi is the default one &noop_backing_dev_info.

Then, generic_fadvise() will just behave as a no-op if sb->s_bdi is
&noop_backing_dev_info, but as the bdev fs (the bdev fs changes
inode_to_bdi() instead), it's actually NOT a pure memfs.

Let's generate a real bdi for erofs_ishare_mnt instead.

Fixes: d86d7817c042 ("erofs: implement .fadvise for page cache share")
Cc: Hongbo Li <lihongbo22 at huawei.com>
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
v2:
 - handle super_setup_bdi() failure properly.

 fs/erofs/ishare.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c
index 829d50d5c717..ec433bacc592 100644
--- a/fs/erofs/ishare.c
+++ b/fs/erofs/ishare.c
@@ -200,8 +200,19 @@ struct inode *erofs_real_inode(struct inode *inode, bool *need_iput)

 int __init erofs_init_ishare(void)
 {
-       erofs_ishare_mnt = kern_mount(&erofs_anon_fs_type);
-       return PTR_ERR_OR_ZERO(erofs_ishare_mnt);
+       struct vfsmount *mnt;
+       int ret;
+
+       mnt = kern_mount(&erofs_anon_fs_type);
+       if (IS_ERR(mnt))
+               return PTR_ERR(mnt);
+       /* generic_fadvise() doesn't work if s_bdi == &noop_backing_dev_info */
+       ret = super_setup_bdi(mnt->mnt_sb);
+       if (ret)
+               kern_unmount(mnt);
+       else
+               erofs_ishare_mnt = mnt;
+       return ret;
 }

 void erofs_exit_ishare(void)
--
2.43.5

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ozlabs.org/pipermail/linux-erofs/attachments/20260324/1d2addf4/attachment.htm>