Messages in this thread Patch in this message | | | From | Manfred Spraul <> | Subject | [PATCH 2/3] ipc/sem.c: increase SEMMSL, SEMMNI, SEMOPM | Date | Mon, 6 Oct 2014 20:32:42 +0200 |
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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> --- include/uapi/linux/sem.h | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/include/uapi/linux/sem.h b/include/uapi/linux/sem.h index 541fce0..dd73b90 100644 --- a/include/uapi/linux/sem.h +++ b/include/uapi/linux/sem.h @@ -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 (SEMMNI*SEMMSL) /* <= 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 */ -- 1.9.3
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