[3.8.y.z extended stable] Patch "ipc, mqueue: remove limits for the amount of system-wide queues" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ipc,mqueue: remove limits for the amount of system-wide queues

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.20.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 9774264673d351b75436f6c7174d2d5b3fce8417 Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <davidlohr at hp.com>
Date: Tue, 25 Feb 2014 15:01:45 -0800
Subject: ipc,mqueue: remove limits for the amount of system-wide queues

commit f3713fd9cff733d9df83116422d8e4af6e86b2bb upstream.

Commit 93e6f119c0ce ("ipc/mqueue: cleanup definition names and
locations") added global hardcoded limits to the amount of message
queues that can be created.  While these limits are per-namespace,
reality is that it ends up breaking userspace applications.
Historically users have, at least in theory, been able to create up to
INT_MAX queues, and limiting it to just 1024 is way too low and dramatic
for some workloads and use cases.  For instance, Madars reports:

 "This update imposes bad limits on our multi-process application.  As
  our app uses approaches that each process opens its own set of queues
  (usually something about 3-5 queues per process).  In some scenarios
  we might run up to 3000 processes or more (which of-course for linux
  is not a problem).  Thus we might need up to 9000 queues or more.  All
  processes run under one user."

Other affected users can be found in launchpad bug #1155695:
  https://bugs.launchpad.net/ubuntu/+source/manpages/+bug/1155695

Instead of increasing this limit, revert it entirely and fallback to the
original way of dealing queue limits -- where once a user's resource
limit is reached, and all memory is used, new queues cannot be created.

Signed-off-by: Davidlohr Bueso <davidlohr at hp.com>
Reported-by: Madars Vitolins <m at silodev.com>
Acked-by: Doug Ledford <dledford at redhat.com>
Cc: Manfred Spraul <manfred at colorfullife.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 include/linux/ipc_namespace.h |  2 --
 ipc/mq_sysctl.c               | 18 ++++++++++++------
 ipc/mqueue.c                  |  6 +++---
 3 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index c4d870b..c8db9ca 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -119,9 +119,7 @@ extern int mq_init_ns(struct ipc_namespace *ns);
  *     the new maximum will handle anyone else.  I may have to revisit this
  *     in the future.
  */
-#define MIN_QUEUESMAX			1
 #define DFLT_QUEUESMAX		      256
-#define HARD_QUEUESMAX		     1024
 #define MIN_MSGMAX			1
 #define DFLT_MSG		       10U
 #define DFLT_MSGMAX		       10
diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
index 383d638..5bb8bfe 100644
--- a/ipc/mq_sysctl.c
+++ b/ipc/mq_sysctl.c
@@ -22,6 +22,16 @@ static void *get_mq(ctl_table *table)
 	return which;
 }

+static int proc_mq_dointvec(ctl_table *table, int write,
+			    void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table mq_table;
+	memcpy(&mq_table, table, sizeof(mq_table));
+	mq_table.data = get_mq(table);
+
+	return proc_dointvec(&mq_table, write, buffer, lenp, ppos);
+}
+
 static int proc_mq_dointvec_minmax(ctl_table *table, int write,
 	void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -33,12 +43,10 @@ static int proc_mq_dointvec_minmax(ctl_table *table, int write,
 					lenp, ppos);
 }
 #else
+#define proc_mq_dointvec NULL
 #define proc_mq_dointvec_minmax NULL
 #endif

-static int msg_queues_limit_min = MIN_QUEUESMAX;
-static int msg_queues_limit_max = HARD_QUEUESMAX;
-
 static int msg_max_limit_min = MIN_MSGMAX;
 static int msg_max_limit_max = HARD_MSGMAX;

@@ -51,9 +59,7 @@ static ctl_table mq_sysctls[] = {
 		.data		= &init_ipc_ns.mq_queues_max,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_mq_dointvec_minmax,
-		.extra1		= &msg_queues_limit_min,
-		.extra2		= &msg_queues_limit_max,
+		.proc_handler	= proc_mq_dointvec,
 	},
 	{
 		.procname	= "msg_max",
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index f3f40dc..f2fa658 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -433,9 +433,9 @@ static int mqueue_create(struct inode *dir, struct dentry *dentry,
 		error = -EACCES;
 		goto out_unlock;
 	}
-	if (ipc_ns->mq_queues_count >= HARD_QUEUESMAX ||
-	    (ipc_ns->mq_queues_count >= ipc_ns->mq_queues_max &&
-	     !capable(CAP_SYS_RESOURCE))) {
+
+	if (ipc_ns->mq_queues_count >= ipc_ns->mq_queues_max &&
+	    !capable(CAP_SYS_RESOURCE)) {
 		error = -ENOSPC;
 		goto out_unlock;
 	}
--
1.8.3.2