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SubjectRe: [RFC] [PATCH] hugetlbfs :shmget with SHM_HUGETLB only works as root
Hi Wli,
I tested your patch. But that is not solving the problem.
If the code change to user_shm_lock() is not a good solution, could
you please suggest a method so that the normal user is able to allocate
the huge pages, if his gid is added to /proc/sys/vm/hugetlb_shm_group

Thanks
Ciju

William Lee Irwin III wrote:
> On Wed, Nov 14, 2007 at 09:31:41AM -0600, aglitke wrote:
>> ... if the user's locked limit (ulimit -l) is set to unlimited, allowed
>> (above) is set to 1. In that case, the second part of that if() is
>> bypassed, and the function grants permission. Therefore, the easy
>> solution is to make sure your user's lock_limit is RLIM_INFINITY.
>
> This function deserves a minor cleanup and a bit more commenting.
>
> Reading user->locked_shm within shmlock_user_lock would be nice, too.
>
> Maybe something like this (untested, uncompiled) would do.
>
>
> -- wli
>
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 7b26560..5f51792 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -234,6 +234,12 @@ asmlinkage long sys_munlockall(void)
> /*
> * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
> * shm segments) get accounted against the user_struct instead.
> + * First, user_shm_lock() checks that the user has permission to lock
> + * enough memory; then if so, the locked shm is accounted to the user's
> + * system-wide state. shmlock_user_lock protects the per-user field
> + * tracking how much locked_shm is in use within the struct user_struct.
> + * shmlock_user_lock is taken early to guard the read-only check that
> + * user->locked_shm is in-bounds against updates to user->locked_shm.
> */
> static DEFINE_SPINLOCK(shmlock_user_lock);
>
> @@ -242,19 +248,22 @@ int user_shm_lock(size_t size, struct user_struct *user)
> unsigned long lock_limit, locked;
> int allowed = 0;
>
> + spin_lock(&shmlock_user_lock);
> locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
> if (lock_limit == RLIM_INFINITY)
> allowed = 1;
> - lock_limit >>= PAGE_SHIFT;
> - spin_lock(&shmlock_user_lock);
> - if (!allowed &&
> - locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
> - goto out;
> - get_uid(user);
> - user->locked_shm += locked;
> - allowed = 1;
> -out:
> + else {
> + lock_limit >>= PAGE_SHIFT;
> + if (locked + user->locked_shm <= lock_limit)
> + allowed = 1;
> + else if (capable(CAP_IPC_LOCK))
> + allowed = 1;
> + }
> + if (allowed) {
> + get_uid(user);
> + user->locked_shm += locked;
> + }
> spin_unlock(&shmlock_user_lock);
> return allowed;
> }

-
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