path: root/ipc
diff options
authorDoug Ledford <dledford@redhat.com>2012-05-31 16:26:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-31 17:49:30 -0700
commit858ee3784e8105467f1f3017f4ece51cb51d4830 (patch)
treec95f55ff8bd29be3a8648acc21118a47b07d117b /ipc
parent93e6f119c0ce8a1bba6e81dc8dd97d67be360844 (diff)
ipc/mqueue: switch back to using non-max values on create
Commit b231cca4381e ("message queues: increase range limits") changed how we create a queue that does not include an attr struct passed to open so that it creates the queue with whatever the maximum values are. However, if the admin has set the maximums to allow flexibility in creating a queue (aka, both a large size and large queue are allowed, but combined they create a queue too large for the RLIMIT_MSGQUEUE of the user), then attempts to create a queue without an attr struct will fail. Switch back to using acceptable defaults regardless of what the maximums are. Note: so far, we only know of a few applications that rely on this behavior (specifically, set the maximums in /proc, then run the application which calls mq_open() without passing in an attr struct, and the application expects the newly created message queue to have the maximum sizes that were set in /proc used on the mq_open() call, and all of those applications that we know of are actually part of regression test suites that were coded to do something like this: for size in 4096 65536 $((1024 * 1024)) $((16 * 1024 * 1024)); do echo $size > /proc/sys/fs/mqueue/msgsize_max mq_open || echo "Error opening mq with size $size" done These test suites that depend on any behavior like this are broken. The concept that programs should rely upon the system wide maximum in order to get their desired results instead of simply using a attr struct to specify what they want is fundamentally unfriendly programming practice for any multi-tasking OS. Fixing this will break those few apps that we know of (and those app authors recognize the brokenness of their code and the need to fix it). However, the following patch "mqueue: separate mqueue default value" allows a workaround in the form of new knobs for the default msg queue creation parameters for any software out there that we don't already know about that might rely on this behavior at the moment. Signed-off-by: Doug Ledford <dledford@redhat.com> Cc: Serge E. Hallyn <serue@us.ibm.com> Cc: Amerigo Wang <amwang@redhat.com> Cc: Joe Korty <joe.korty@ccur.com> Cc: Jiri Slaby <jslaby@suse.cz> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
1 files changed, 3 insertions, 2 deletions
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index a2757d4ab77..b103022179a 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -144,8 +144,9 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
info->qsize = 0;
info->user = NULL; /* set when all is ok */
memset(&info->attr, 0, sizeof(info->attr));
- info->attr.mq_maxmsg = ipc_ns->mq_msg_max;
- info->attr.mq_msgsize = ipc_ns->mq_msgsize_max;
+ info->attr.mq_maxmsg = min(ipc_ns->mq_msg_max, DFLT_MSG);
+ info->attr.mq_msgsize =
+ min(ipc_ns->mq_msgsize_max, DFLT_MSGSIZE);
if (attr) {
info->attr.mq_maxmsg = attr->mq_maxmsg;
info->attr.mq_msgsize = attr->mq_msgsize;