30.01.2013 02:57, J. Bruce Fields пишет:
On Tue, Jan 29, 2013 at 02:03:30PM +0300, Stanislav Kinsbursky wrote:
There could be a service transport, which is processed by service thread and
racing in the same time with per-net service shutdown like listed below:
CPU#0: CPU#1:
svc_recv svc_close_net
svc_get_next_xprt (list_del_init(xpt_ready))
svc_close_list (set XPT_BUSY and XPT_CLOSE)
svc_clear_pools(xprt was gained on CPU#0 already)
svc_delete_xprt (set XPT_DEAD)
svc_handle_xprt (is XPT_CLOSE => svc_delete_xprt()
BUG()
There could be different solutions of the problem.
Probably, the patch doesn't implement the best one, but I hope the simple one.
IOW, it protects critical section (dequeuing of pending transport and
enqueuing it back to the pool) by per-service rw semaphore,
It's actually per-thread (per-struct svc_rqst) here.
Yes, sure.
taken for read.
On per-net transports shutdown, this semaphore have to be taken for write.
There's no down_write in this patch. Did you forget this part?
See "fs/nfs/callback.c" part
The server rpc code goes to some care not to write to any global
structure, to prevent server threads running on multiple cores from
bouncing cache lines between them.
This is just an idea. I.e. I wasn't trying to polish the patch - just to share the vision.
But my understanding is that even down_read() does modify the semaphore.
So we might want something like the percpu semaphore describe in
Documentation/percpu-rw-semaphore.txt.
Sure, I'll have a look.
--
Best regards,
Stanislav Kinsbursky
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