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fs: nfs: fix missing refcnt by replacing folio_set_private by folio_attach_private

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This patch is inspired by a code review of fs codes which aims at
folio's extra refcnt that could introduce unwanted behavious when
judging refcnt, such as[1].That is, the folio passed to
mapping_evict_folio carries the refcnts from find_lock_entries,
page_cache, corresponding to PTEs and folio's private if has. However,
current code doesn't take the refcnt for folio's private which could
have mapping_evict_folio miss the one to only PTE and lead to
call filemap_release_folio wrongly.

[1]
long mapping_evict_folio(struct address_space *mapping, struct folio *folio)
{
...
//current code will misjudge here if there is one pte on the folio which
is be deemed as the one as folio's private
        if (folio_ref_count(folio) >
                        folio_nr_pages(folio) + folio_has_private(folio) + 1)
                return 0;
        if (!filemap_release_folio(folio, 0))
                return 0;

        return remove_mapping(mapping, folio);
}

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
This commit is contained in:
Zhaoyang Huang 2024-08-30 11:27:47 +08:00 committed by Anna Schumaker
parent 40c80881eb
commit 03e02b9417
1 changed files with 2 additions and 4 deletions
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6
fs/nfs/write.c
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@ -772,8 +772,7 @@ static void nfs_inode_add_request(struct nfs_page *req)
nfs_lock_request(req);
spin_lock(&mapping->i_private_lock);
set_bit(PG_MAPPED, &req->wb_flags);
folio_set_private(folio);
folio->private = req;
folio_attach_private(folio, req);
spin_unlock(&mapping->i_private_lock);
atomic_long_inc(&nfsi->nrequests);
/* this a head request for a page group - mark it as having an
@ -797,8 +796,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
spin_lock(&mapping->i_private_lock);
if (likely(folio)) {
folio->private = NULL;
folio_clear_private(folio);
folio_detach_private(folio);
clear_bit(PG_MAPPED, &req->wb_head->wb_flags);
}
spin_unlock(&mapping->i_private_lock);