From: Manfred Spraul <manfred@colorfullife.com>
To: Davidlohr Bueso <davidlohr@hp.com>, akpm@linux-foundation.org
Cc: aswin@hp.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] ipc,msg: loosen check for full queue
Date: Wed, 14 May 2014 20:00:25 +0200 [thread overview]
Message-ID: <5373AF39.7030406@colorfullife.com> (raw)
In-Reply-To: <1400012857-11733-6-git-send-email-davidlohr@hp.com>
Hi Davidlohr, Hi Andrew,
On 05/13/2014 10:27 PM, Davidlohr Bueso wrote:
> When sending a message, we must guarantee that there will be
> enough room in the queue to add it, otherwise wait until space
> becomes available -- which requires blocking the calling task.
> Currently, this relies meeting both of the following conditions:
>
> (i) The new msg size + current size is lower than the queue's max size.
> (ii) The current amount of messages in the queue + 1 (this msg) is lower
> than the queue's max size.
>
> While (i) is obvious and well documented in the msgsnd(2) manpage, the
> second one is far more ambiguous and does not serve the purpose, as we do
> not control the amount of messages in the queue (unlike posix queues do).
> Thus remove (ii) and loosen how we check for space.
I know that (ii) is undocumented and not part of SUS, but I think it is
required:
Otherwise it would be possible to use up an infinite amount of locked
memory by sending 0-byte messages.
I added it some long time ago, and at that time I didn't check what the
other sysv msg implementation were doing.
From a quick search:
FreeBSD:
- Optional: RACCT_MSGQQUEUED
- Always: The number of messages is limited due to a global array
(limited to MSGTQL entries: array msghdrs, free list free_msghdrs)
http://fxr.watson.org/fxr/source/kern/sysv_msg.c
Opensolaris:
- Also a limit of the number of messages:
http://fxr.watson.org/fxr/source/common/os/msg.c?v=OPENSOLARIS;im=bigexcerpts#L1166
- it appears that it is related to MSGTQL:
http://fxr.watson.org/fxr/source/common/os/msg.c?v=OPENSOLARIS;im=bigexcerpts#L652
I.e.: We cannot remove the check unless we add another mechanism that
limits the number of messages.
--
Manfred
next prev parent reply other threads:[~2014-05-14 18:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-13 20:27 [PATCH -next 0/5] ipc,msg: fixes and updates Davidlohr Bueso
2014-05-13 20:27 ` [PATCH 1/5] ipc,msg: use current->state helpers Davidlohr Bueso
2014-05-17 17:55 ` Manfred Spraul
2014-05-13 20:27 ` [PATCH 2/5] ipc,msg: move some msgq ns code around Davidlohr Bueso
2014-05-17 17:57 ` Manfred Spraul
2014-05-13 20:27 ` [PATCH 3/5] ipc,msg: always respect MSG_NOERROR Davidlohr Bueso
2014-05-18 5:53 ` Manfred Spraul
2014-05-18 18:01 ` Davidlohr Bueso
2014-05-19 18:01 ` Manfred Spraul
2014-05-13 20:27 ` [PATCH 4/5] ipc,msg: document volatile r_msg Davidlohr Bueso
2014-05-18 6:08 ` Manfred Spraul
2014-05-13 20:27 ` [PATCH 5/5] ipc,msg: loosen check for full queue Davidlohr Bueso
2014-05-14 18:00 ` Manfred Spraul [this message]
2014-05-14 19:50 ` Davidlohr Bueso
2014-05-15 4:20 ` Manfred Spraul
2014-05-15 15:46 ` Davidlohr Bueso
2014-05-16 12:47 ` Michael Kerrisk (man-pages)
2014-05-18 18:16 ` Davidlohr Bueso
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=5373AF39.7030406@colorfullife.com \
--to=manfred@colorfullife.com \
--cc=akpm@linux-foundation.org \
--cc=aswin@hp.com \
--cc=davidlohr@hp.com \
--cc=linux-kernel@vger.kernel.org \
/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).