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Date:   Fri, 18 Sep 2020 20:50:52 +0800
From:   <zhe.he@...driver.com>
To:     <bfields@...ldses.org>, <chuck.lever@...cle.com>,
        <trond.myklebust@...merspace.com>, <anna.schumaker@...app.com>,
        <davem@...emloft.net>, <kuba@...nel.org>,
        <linux-nfs@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <zhe.he@...driver.com>
Subject: [PATCH] SUNRPC: Flush dcache only when receiving more seeking

From: He Zhe <zhe.he@...driver.com>

commit ca07eda33e01 ("SUNRPC: Refactor svc_recvfrom()") introduces
svc_flush_bvec to after sock_recvmsg, but sometimes we receive less than we
seek, which triggers the following warning.

WARNING: CPU: 0 PID: 18266 at include/linux/bvec.h:101 bvec_iter_advance+0x44/0xa8
Attempted to advance past end of bvec iter
Modules linked in: sch_fq_codel openvswitch nsh nf_conncount nf_nat
nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4
CPU: 1 PID: 18266 Comm: nfsd Not tainted 5.9.0-rc5 #1
Hardware name: Xilinx Zynq Platform
[<80112ec0>] (unwind_backtrace) from [<8010c3a8>] (show_stack+0x18/0x1c)
[<8010c3a8>] (show_stack) from [<80755214>] (dump_stack+0x9c/0xd0)
[<80755214>] (dump_stack) from [<80125e64>] (__warn+0xdc/0xf4)
[<80125e64>] (__warn) from [<80126244>] (warn_slowpath_fmt+0x84/0xac)
[<80126244>] (warn_slowpath_fmt) from [<80c88514>] (bvec_iter_advance+0x44/0xa8)
[<80c88514>] (bvec_iter_advance) from [<80c88940>] (svc_tcp_read_msg+0x10c/0x1bc)
[<80c88940>] (svc_tcp_read_msg) from [<80c895d4>] (svc_tcp_recvfrom+0x98/0x63c)
[<80c895d4>] (svc_tcp_recvfrom) from [<80c97bf4>] (svc_handle_xprt+0x48c/0x4f8)
[<80c97bf4>] (svc_handle_xprt) from [<80c98038>] (svc_recv+0x94/0x1e0)
[<80c98038>] (svc_recv) from [<804747cc>] (nfsd+0xf0/0x168)
[<804747cc>] (nfsd) from [<80148a0c>] (kthread+0x144/0x154)
[<80148a0c>] (kthread) from [<80100114>] (ret_from_fork+0x14/0x20)

Fixes: ca07eda33e01 ("SUNRPC: Refactor svc_recvfrom()")
Cc: <stable@...r.kernel.org> # 5.8+
Signed-off-by: He Zhe <zhe.he@...driver.com>
---
 net/sunrpc/svcsock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index d5805fa1d066..ea3bc9635448 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -277,7 +277,7 @@ static ssize_t svc_tcp_read_msg(struct svc_rqst *rqstp, size_t buflen,
 		buflen -= seek;
 	}
 	len = sock_recvmsg(svsk->sk_sock, &msg, MSG_DONTWAIT);
-	if (len > 0)
+	if (len > (seek & PAGE_MASK))
 		svc_flush_bvec(bvec, len, seek);
 
 	/* If we read a full record, then assume there may be more
-- 
2.17.1

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