On Tue, 9 Apr 2013 21:39:24 -0500 Robin Holt <h...@sgi.com> wrote:
> Trying to run an application which was trying to put data into half
> of memory using shmget(), we found that having a shmall value below
> 8EiB-8TiB would prevent us from using anything more than 8TiB. By setting
> kernel.shmall greater that 8EiB-8TiB would make the job work.
>
> In the newseg() function, ns->shm_tot which, at 8TiB is INT_MAX.
You have way too much memory.
> ipc/shm.c:
> 458 static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
> 459 {
> ...
> 465 int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
> ...
> 474 if (ns->shm_tot + numpages > ns->shm_ctlall)
> 475 return -ENOSPC;
>
> ...
>
> --- a/include/linux/ipc_namespace.h
> +++ b/include/linux/ipc_namespace.h
> @@ -43,8 +43,8 @@ struct ipc_namespace {
>
> size_t shm_ctlmax;
> size_t shm_ctlall;
> + unsigned long shm_tot;
> int shm_ctlmni;
> - int shm_tot;
> /*
> * Defines whether IPC_RMID is forced for _all_ shm segments regardless
> * of shmctl()
I reviewed everything for fallout from this and don't see any obvious
issues.
I do wonder about the appropriateness of the unsigned long type. Most
(but by no means all) code in this area uses size_t, and the
above-quoted ns->shm_ctlall is size_t.
And the above-quoted num_pages is `int'. Both the size and signedness
of `int' make no sense - what happens if the incoming ipc_params.u.size
is >2G?
So I'll add this, and ask whether ipc_namespace.shm_tot should be size_t?
--- a/ipc/shm.c~ipc-sysv-shared-memory-limited-to-8tib-fix
+++ a/ipc/shm.c
@@ -462,7 +462,7 @@ static int newseg(struct ipc_namespace *
size_t size = params->u.size;
int error;
struct shmid_kernel *shp;
- int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
+ size_t numpages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
struct file * file;
char name[13];
int id;
_
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