Messages in this thread | | | Date | Wed, 30 Jan 2013 09:42:14 +0400 | From | Stanislav Kinsbursky <> | Subject | Re: [RFC PATCH] SUNRPC: protect transport processing with rw sem |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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