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Subject[PATCH] ipc,mqueue: remove limits for the amount of system-wide queues
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From: Davidlohr Bueso <davidlohr@hp.com>

Commit 93e6f119 (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.

Reported-by: m@silodev.com
Cc: Doug Ledford <dledford@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Davidlohr Bueso <davidlohr@hp.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 e7831d2..35e7eca 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 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 ccf1f9f..c3b3117 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;
}
--
1.8.1.4




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