[bpf-next,1/4] xsk: avoid store-tearing when assigning queues
diff mbox series

Message ID 20190822091306.20581-2-bjorn.topel@gmail.com
State Changes Requested
Delegated to: BPF Maintainers
Headers show
Series
  • xsk: various CPU barrier and {READ, WRITE}_ONCE fixes
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Commit Message

Björn Töpel Aug. 22, 2019, 9:13 a.m. UTC
From: Björn Töpel <bjorn.topel@intel.com>

Use WRITE_ONCE when doing the store of tx, rx, fq, and cq, to avoid
potential store-tearing. These members are read outside of the control
mutex in the mmap implementation.

Fixes: 37b076933a8e ("xsk: add missing write- and data-dependency barrier")
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
 net/xdp/xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Björn Töpel Aug. 22, 2019, 1:51 p.m. UTC | #1
On Thu, 22 Aug 2019 at 15:26, Hillf Danton <hdanton@sina.com> wrote:
>
> >
>
> >    /* Make sure queue is ready before it can be seen by others */
>
> >    smp_wmb();
>
>
>
> Hehe, who put mb here and for what?
>

That was from an earlier commit, and it's a barrier paired with the
lock-less reading of queues in xsk_mmap. Uhm... not sure I answered
your question?


Björn




>
>
> >-   *queue = q;
>
> >+  WRITE_ONCE(*queue, q);
>
> >    return 0;
>
>
Jonathan Lemon Aug. 23, 2019, 4:43 p.m. UTC | #2
On 22 Aug 2019, at 2:13, Björn Töpel wrote:

> From: Björn Töpel <bjorn.topel@intel.com>
>
> Use WRITE_ONCE when doing the store of tx, rx, fq, and cq, to avoid
> potential store-tearing. These members are read outside of the control
> mutex in the mmap implementation.
>
> Fixes: 37b076933a8e ("xsk: add missing write- and data-dependency barrier")
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>

Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>

Patch
diff mbox series

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index ee4428a892fa..f3351013c2a5 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -409,7 +409,7 @@  static int xsk_init_queue(u32 entries, struct xsk_queue **queue,
 
 	/* Make sure queue is ready before it can be seen by others */
 	smp_wmb();
-	*queue = q;
+	WRITE_ONCE(*queue, q);
 	return 0;
 }