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

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@hp.com>
Reported-by: Madars Vitolins <m@silodev.com>
Acked-by: Doug Ledford <dledford@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: <stable@vger.kernel.org>	[3.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 15 insertions, 11 deletions

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index e7831d203737..35e7eca4e33b 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -118,9 +118,7 @@ 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 383d638340b8..5bb8bfe67149 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 ccf1f9fd263a..c3b31179122c 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;
         }