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Date:   Mon, 11 Feb 2019 08:15:29 -0800
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>,
        Bjorn Topel <bjorn.topel@intel.com>,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        netdev@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH v2] xsk: share the mmap_sem for page pinning
Message-ID: <20190211161529.uskq5ca7y3j5522i@linux-r8p5>
Mail-Followup-To: akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>,
        Bjorn Topel <bjorn.topel@intel.com>,
        Magnus Karlsson <magnus.karlsson@intel.com>, netdev@vger.kernel.org,
        Davidlohr Bueso <dbueso@suse.de>
References: <20190207053740.26915-1-dave@stgolabs.net>
 <20190207053740.26915-2-dave@stgolabs.net>
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Holding mmap_sem exclusively for a gup() is an overkill.
Lets share the lock and replace the gup call for gup_longterm(),
as it is better suited for the lifetime of the pinning.

Cc: David S. Miller <davem@davemloft.net>
Cc: Bjorn Topel <bjorn.topel@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@intel.com>
CC: netdev@vger.kernel.org
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
 net/xdp/xdp_umem.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
index 5ab236c5c9a5..e7fa8d0d7090 100644
--- a/net/xdp/xdp_umem.c
+++ b/net/xdp/xdp_umem.c
@@ -265,10 +265,10 @@ static int xdp_umem_pin_pages(struct xdp_umem *umem)
 	if (!umem->pgs)
 		return -ENOMEM;
 
-	down_write(&current->mm->mmap_sem);
-	npgs = get_user_pages(umem->address, umem->npgs,
+	down_read(&current->mm->mmap_sem);
+	npgs = get_user_pages_longterm(umem->address, umem->npgs,
 			      gup_flags, &umem->pgs[0], NULL);
-	up_write(&current->mm->mmap_sem);
+	up_read(&current->mm->mmap_sem);
 
 	if (npgs != umem->npgs) {
 		if (npgs >= 0) {
-- 
2.16.4