From 858ee3784e8105467f1f3017f4ece51cb51d4830 Mon Sep 17 00:00:00 2001 From: Doug Ledford Date: Thu, 31 May 2012 16:26:29 -0700 Subject: [PATCH] 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 Cc: Serge E. Hallyn Cc: Amerigo Wang Cc: Joe Korty Cc: Jiri Slaby Acked-by: KOSAKI Motohiro Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/ipc_namespace.h | 2 ++ ipc/mqueue.c | 5 +++-- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index 1372b566e1e1..bde094ee7b0e 100644 --- a/include/linux/ipc_namespace.h +++ b/include/linux/ipc_namespace.h @@ -95,9 +95,11 @@ extern int mq_init_ns(struct ipc_namespace *ns); #define DFLT_QUEUESMAX 256 /* max number of message queues */ #define HARD_QUEUESMAX 1024 #define MIN_MSGMAX 1 +#define DFLT_MSG 10U #define DFLT_MSGMAX 10 /* max number of messages in each queue */ #define HARD_MSGMAX (32768*sizeof(void *)/4) #define MIN_MSGSIZEMAX 128 +#define DFLT_MSGSIZE 8192U #define DFLT_MSGSIZEMAX 8192 /* max message size */ #define HARD_MSGSIZEMAX (8192*128) #else diff --git a/ipc/mqueue.c b/ipc/mqueue.c index a2757d4ab773..b103022179a3 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; -- 2.20.1