Messages in this thread | | | Subject | Re: [PATCHv2] vsock: Fix blocking ops call in prepare_to_wait | From | Laura Abbott <> | Date | Mon, 14 Mar 2016 13:07:06 -0700 |
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On 03/14/2016 12:24 PM, David Miller wrote: > From: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com> > Date: Fri, 11 Mar 2016 13:39:23 +0100 > >> I think I found a problem with the patch submitted by Laura Abbott >> ( https://lkml.org/lkml/2016/2/4/711 ): we might miss wakeups. >> Since the condition is not checked between the prepare_to_wait and the >> schedule(), if a wakeup happens after the condition is checked but before >> the sleep happens, and we miss it. ( A description of the problem can be >> found here: http://www.makelinux.net/ldd3/chp-6-sect-2 ). >> >> My solution (see patch below) is to shrink the area influenced by >> prepare_to_wait, but keeping the fragile section around the condition, and >> keep the rest of the code in "normal" running state. This way the sleep is >> correct and the other functions don't need to worry. The only caveat here >> is that the function(s) called to verify the conditions are really not >> allowed to sleep, so if you need synchronization in the backend of e.g. >> vsock_stream_has_space(), you should use spinlocks and not mutexes. >> >> In case we want to be able to sleep while waiting for conditions, we can >> consider this instead: https://lwn.net/Articles/628628/ . >> >> >> I stumbled on this problem while working on fixing the upcoming virtio >> backend for vsock, below is the patch I had prepared, with the original >> message. > > Can someone please look at this? Who maintains this code anyways? >
Nobody was listed in MAINTAINERS. I tried cc-ing some of the e-mail addresses of the original authors (vmware?) when sending the original patch and they all bounced.
Thanks, Laura
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