From: David Miller <davem@davemloft.net>
To: sunilmut@microsoft.com
Cc: kys@microsoft.com, haiyangz@microsoft.com,
sthemmin@microsoft.com, sashal@kernel.org, decui@microsoft.com,
mikelley@microsoft.com, netdev@vger.kernel.org,
linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v2] hvsock: fix epollout hang from race condition
Date: Tue, 18 Jun 2019 21:42:32 -0400 (EDT) [thread overview]
Message-ID: <20190618.214232.430281845003030631.davem@davemloft.net> (raw)
In-Reply-To: <MW2PR2101MB111670139C7F5DC567129DD3C0EB0@MW2PR2101MB1116.namprd21.prod.outlook.com>
From: Sunil Muthuswamy <sunilmut@microsoft.com>
Date: Mon, 17 Jun 2019 19:26:25 +0000
> Currently, hvsock can enter into a state where epoll_wait on EPOLLOUT will
> not return even when the hvsock socket is writable, under some race
> condition. This can happen under the following sequence:
...
> Now, the EPOLLOUT will never return even if the socket write buffer is
> empty.
>
> The fix is to set the pending size to the default size and never change it.
> This way the host will always notify the guest whenever the writable space
> is bigger than the pending size. The host is already optimized to *only*
> notify the guest when the pending size threshold boundary is crossed and
> not everytime.
>
> This change also reduces the cpu usage somewhat since hv_stream_has_space()
> is in the hotpath of send:
> vsock_stream_sendmsg()->hv_stream_has_space()
> Earlier hv_stream_has_space was setting/clearing the pending size on every
> call.
>
> Signed-off-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> Reviewed-by: Dexuan Cui <decui@microsoft.com>
> ---
> - Resubmitting the patch after taking care of some spurious warnings.
Applied and queued up for -stable.
prev parent reply other threads:[~2019-06-19 1:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-17 19:26 [PATCH net v2] hvsock: fix epollout hang from race condition Sunil Muthuswamy
2019-06-19 1:42 ` David Miller [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190618.214232.430281845003030631.davem@davemloft.net \
--to=davem@davemloft.net \
--cc=decui@microsoft.com \
--cc=haiyangz@microsoft.com \
--cc=kys@microsoft.com \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mikelley@microsoft.com \
--cc=netdev@vger.kernel.org \
--cc=sashal@kernel.org \
--cc=sthemmin@microsoft.com \
--cc=sunilmut@microsoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).