linux-kernel - Re: [Phishing Risk] [External] [PATCH] erofs: fix missing xas

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Message-ID: <1bcb11ad-e2e0-6c0d-659e-1b20b6b99fb1@bytedance.com>
Date:   Mon, 14 Nov 2022 14:27:50 +0800
From:   Jia Zhu <zhujia.zj@...edance.com>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>, xiang@...nel.org,
        chao@...nel.org, yinxin.x@...edance.com,
        linux-erofs@...ts.ozlabs.org
Cc:     dhowells@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [Phishing Risk] [External] [PATCH] erofs: fix missing xas_retry()
 in fscache mode

在 2022/11/11 17:08, Jingbo Xu 写道:
> The xarray iteration only holds RCU and thus may encounter
> XA_RETRY_ENTRY if there's process modifying the xarray concurrently.
> This will cause oops when referring to the invalid entry.
> 
> Fix this by adding the missing xas_retry(), which will make the
> iteration wind back to the root node if XA_RETRY_ENTRY is encountered.
> 
> Fixes: d435d53228dd ("erofs: change to use asynchronous io for fscache readpage/readahead")
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
Reviewed-by: Jia Zhu <zhujia.zj@...edance.com>
> ---
>   fs/erofs/fscache.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index fe05bc51f9f2..458c1c70ef30 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -75,11 +75,15 @@ static void erofs_fscache_rreq_unlock_folios(struct netfs_io_request *rreq)
>   
>   	rcu_read_lock();
>   	xas_for_each(&xas, folio, last_page) {
> -		unsigned int pgpos =
> -			(folio_index(folio) - start_page) * PAGE_SIZE;
> -		unsigned int pgend = pgpos + folio_size(folio);
> +		unsigned int pgpos, pgend;
>   		bool pg_failed = false;
>   
> +		if (xas_retry(&xas, folio))
> +			continue;
> +
> +		pgpos = (folio_index(folio) - start_page) * PAGE_SIZE;
> +		pgend = pgpos + folio_size(folio);
> +
>   		for (;;) {
>   			if (!subreq) {
>   				pg_failed = true;