Commit e843e7d2 authored Dec 12, 2014 by Manfred Spraul Committed by Linus Torvalds Dec 13, 2014

ipc/sem.c: increase SEMMSL, SEMMNI, SEMOPM



a)

SysV can be abused to allocate locked kernel memory.  For most systems, a
small limit doesn't make sense, see the discussion with regards to SHMMAX.

Therefore: Increase the sysv sem limits so that all known applications
will work with these defaults.

b)

With regards to the maximum supported:
Some of the specified hard limits are not correct anymore, therefore the
patch updates the documentation.

- SEMMNI must stay below IPCMNI, which is 32768.
  As for SHMMAX: Stay a bit below this limit.

- SEMMSL was limited to 8k, to ensure that the kmalloc for the kernel array
  was limited to 16 kB (order=2)

  This doesn't apply anymore:
   - the allocation size isn't sizeof(short)*nsems anymore.
   - ipc_alloc falls back to vmalloc

- SEMOPM should stay below 1000, to limit the kmalloc in semtimedop() to an
  order=1 allocation.
  Therefore: Leave it at 500 (order=0 allocation).

Note:
If an administrator must limit the memory allocations, then he can set the
values as necessary.

Or he can disable sysv entirely (as e.g. done by Android).

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2e094abf

include/uapi/linux/sem.h

+15 −3

Original line number	Diff line number	Diff line
		@@ -63,10 +63,22 @@ struct seminfo {
		int semaem;
		};

		#define SEMMNI 128 /* <= IPCMNI max # of semaphore identifiers */
		#define SEMMSL 250 /* <= 8 000 max num of semaphores per id */
		/*
		* SEMMNI, SEMMSL and SEMMNS are default values which can be
		* modified by sysctl.
		* The values has been chosen to be larger than necessary for any
		* known configuration.
		*
		* SEMOPM should not be increased beyond 1000, otherwise there is the
		* risk that semop()/semtimedop() fails due to kernel memory fragmentation when
		* allocating the sop array.
		*/


		#define SEMMNI 32000 /* <= IPCMNI max # of semaphore identifiers */
		#define SEMMSL 32000 /* <= INT_MAX max num of semaphores per id */
		#define SEMMNS (SEMMNISEMMSL) / <= INT_MAX max # of semaphores in system */
		#define SEMOPM 32 /* <= 1 000 max num of ops per semop call */
		#define SEMOPM 500 /* <= 1 000 max num of ops per semop call */
		#define SEMVMX 32767 /* <= 32767 semaphore maximum value */
		#define SEMAEM SEMVMX /* adjust on exit max value */