On Fri, 2014-04-11 at 20:28 +0200, Manfred Spraul wrote:
> Hi Davidlohr,
>
> On 04/03/2014 02:20 AM, Davidlohr Bueso wrote:
> > The default size for shmmax is, and always has been, 32Mb.
> > Today, in the XXI century, it seems that this value is rather small,
> > making users have to increase it via sysctl, which can cause
> > unnecessary work and userspace application workarounds[1].
> >
> > [snip]
> > Running this patch through LTP, everything passes, except the following,
> > which, due to the nature of this change, is quite expected:
> >
> > shmget02 1 TFAIL : call succeeded unexpectedly
> Why is this TFAIL expected?
So looking at shmget02.c, this is the case that fails:
for (i = 0; i < TST_TOTAL; i++) {
/*
* Look for a failure ...
*/
TEST(shmget(*(TC[i].skey), TC[i].size, TC[i].flags));
if (TEST_RETURN != -1) {
tst_resm(TFAIL, "call succeeded unexpectedly");
continue;
}
Where TC[0] is:
struct test_case_t {
int *skey;
int size;
int flags;
int error;
} TC[] = {
/* EINVAL - size is 0 */
{
&shmkey2, 0, IPC_CREAT | IPC_EXCL | SHM_RW, EINVAL},
So it's expected because now 0 is actually valid. And before:
EINVAL A new segment was to be created and size < SHMMIN or size > SHMMAX
> >
> > diff --git a/ipc/shm.c b/ipc/shm.c
> > index 7645961..ae01ffa 100644
> > --- a/ipc/shm.c
> > +++ b/ipc/shm.c
> > @@ -490,10 +490,12 @@ static int newseg(struct ipc_namespace *ns, struct
> > ipc_params *params)
> > int id;
> > vm_flags_t acctflag = 0;
> >
> > - if (size < SHMMIN || size > ns->shm_ctlmax)
> > + if (ns->shm_ctlmax &&
> > + (size < SHMMIN || size > ns->shm_ctlmax))
> > return -EINVAL;
> >
> > - if (ns->shm_tot + numpages > ns->shm_ctlall)
> > + if (ns->shm_ctlall &&
> > + ns->shm_tot + numpages > ns->shm_ctlall)
> > return -ENOSPC;
> >
> > shp = ipc_rcu_alloc(sizeof(*shp));
> Ok, I understand it:
> Your patch disables checking shmmax, shmall *AND* checking for SHMMIN.
Right, if shmmax is 0, then there's no point checking for shmmin,
otherwise we'd always end up returning EINVAL.
>
> a) Have you double checked that 0-sized shm segments work properly?
> Does the swap code handle it properly, ...? EINVAL A new segment was to be
> created and size < SHMMIN or size > SHMMAX
Hmm so I've been using this patch just fine on my laptop since I sent
it. So far I haven't seen any issues. Are you refering to something in
particular? I'd be happy to run any cases you're concerned with.
> b) It's that yet another risk for user space incompatibility?
Sorry, I don't follow here.
> c) The patch summary is misleading, the impact on SHMMIN is not mentioned.
Sure, I can explicitly add it to the changelog.
Thanks,
Davidlohr
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