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SubjectRe: [PATCH v1] erofs: fix refcount on the metabuf used for inode lookup
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Hi Sandeep,

On 2024/2/21 03:11, Sandeep Dhavale wrote:
> In erofs_find_target_block() when erofs_dirnamecmp() returns 0,
> we do not assign the target metabuf. This causes the caller
> erofs_namei()'s erofs_put_metabuf() at the end to be not effective
> leaving the refcount on the page.
> As the page from metabuf (buf->page) is never put, such page cannot be
> migrated or reclaimed. Fix it now by putting the metabuf from
> previous loop and assigning the current metabuf to target before
> returning so caller erofs_namei() can do the final put as it was
> intended.
>
> Fixes: 500edd095648 ("erofs: use meta buffers for inode lookup")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sandeep Dhavale <dhavale@google.com>

Many thanks for the catch!

> ---
> fs/erofs/namei.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/erofs/namei.c b/fs/erofs/namei.c
> index d4f631d39f0f..bfe1c926436b 100644
> --- a/fs/erofs/namei.c
> +++ b/fs/erofs/namei.c
> @@ -132,7 +132,10 @@ static void *erofs_find_target_block(struct erofs_buf *target,
>
> if (!diff) {
> *_ndirents = 0;
> - goto out;
> + if (!IS_ERR(candidate))
> + erofs_put_metabuf(target);
> + *target = buf;
> + return de;
> } else if (diff > 0) {
> head = mid + 1;
> startprfx = matched;

The fix is correct, yet I tend to try to reorganize this snippet for
simplicity, how about the following diff (untested)?

If it looks good to you, could you resend a formal patch? Thanks!

Thanks,
Gao Xiang

fs/erofs/namei.c | 29 ++++++++++++++---------------
1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/fs/erofs/namei.c b/fs/erofs/namei.c
index d4f631d39f0f..9fb2d627578e 100644
--- a/fs/erofs/namei.c
+++ b/fs/erofs/namei.c
@@ -129,25 +129,24 @@ static void *erofs_find_target_block(struct erofs_buf *target,

/* string comparison without already matched prefix */
diff = erofs_dirnamecmp(name, &dname, &matched);
-
- if (!diff) {
- *_ndirents = 0;
- goto out;
- } else if (diff > 0) {
- head = mid + 1;
- startprfx = matched;
-
- if (!IS_ERR(candidate))
- erofs_put_metabuf(target);
- *target = buf;
- candidate = de;
- *_ndirents = ndirents;
- } else {
+ if (diff < 0) {
erofs_put_metabuf(&buf);
-
back = mid - 1;
endprfx = matched;
+ continue;
}
+
+ if (!IS_ERR(candidate))
+ erofs_put_metabuf(target);
+ *target = buf;
+ if (!diff) {
+ *_ndirents = 0;
+ return de;
+ }
+ head = mid + 1;
+ startprfx = matched;
+ candidate = de;
+ *_ndirents = ndirents;
continue;
}
out: /* free if the candidate is valid */
--
2.39.3
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