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Subject[PATCH 4.19 186/639] xsk: add missing smp_rmb() in xsk_mmap
From: Magnus Karlsson <>

[ Upstream commit e6762c8bcf982821935a2b1cb33cf8335d0eefae ]

All the setup code in AF_XDP is protected by a mutex with the
exception of the mmap code that cannot use it. To make sure that a
process banging on the mmap call at the same time as another process
is setting up the socket, smp_wmb() calls were added in the umem
registration code and the queue creation code, so that the published
structures that xsk_mmap needs would be consistent. However, the
corresponding smp_rmb() calls were not added to the xsk_mmap
code. This patch adds these calls.

Fixes: 37b076933a8e3 ("xsk: add missing write- and data-dependency barrier")
Fixes: c0c77d8fb787c ("xsk: add user memory registration support sockopt")
Signed-off-by: Magnus Karlsson <>
Signed-off-by: Alexei Starovoitov <>
Signed-off-by: Sasha Levin <>
net/xdp/xsk.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index ff15207036dc5..547fc4554b22c 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -661,6 +661,8 @@ static int xsk_mmap(struct file *file, struct socket *sock,
if (!umem)
return -EINVAL;

+ /* Matches the smp_wmb() in XDP_UMEM_REG */
+ smp_rmb();
q = READ_ONCE(umem->fq);
@@ -670,6 +672,8 @@ static int xsk_mmap(struct file *file, struct socket *sock,
if (!q)
return -EINVAL;

+ /* Matches the smp_wmb() in xsk_init_queue */
+ smp_rmb();
qpg = virt_to_head_page(q->ring);
if (size > (PAGE_SIZE << compound_order(qpg)))
return -EINVAL;

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