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    SubjectRe: [patch 1/2] mm: Fix SHM_HUGETLB to work with users in hugetlb_shm_group
    On Fri, Feb 20, 2009 at 05:54:57PM -0800, Ravikiran G Thirumalai wrote:
    > This is a two patch series to fix a long standing inconsistency with the
    > mechanism to allow non root users allocate hugetlb shm. The patch changelog
    > is self explanatory. Here's a link to the previous discussion as well:
    >
    > http://lkml.org/lkml/2009/2/10/89
    >
    > ---
    > Fix hugetlb subsystem so that non root users belonging to hugetlb_shm_group
    > can actually allocate hugetlb backed shm.
    >
    > Currently non root users cannot even map one large page using SHM_HUGETLB
    > when they belong to the gid in /proc/sys/vm/hugetlb_shm_group.
    > This is because allocation size is verified against RLIMIT_MEMLOCK resource
    > limit even if the user belongs to hugetlb_shm_group.
    >
    > This patch
    > 1. Fixes hugetlb subsystem so that users with CAP_IPC_LOCK and users
    > belonging to hugetlb_shm_group don't need to be restricted with
    > RLIMIT_MEMLOCK resource limits
    > 2. This patch also disables mlock based rlimit checking (which will
    > be reinstated and marked deprecated in a subsequent patch).
    >
    > Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
    > Cc: Mel Gorman <mel@csn.ul.ie>
    > Cc: Wli <wli@movementarian.org>
    >
    > Index: linux-2.6-tip/fs/hugetlbfs/inode.c
    > ===================================================================
    > --- linux-2.6-tip.orig/fs/hugetlbfs/inode.c 2009-02-10 13:24:56.000000000 -0800
    > +++ linux-2.6-tip/fs/hugetlbfs/inode.c 2009-02-10 13:30:05.000000000 -0800
    > @@ -942,9 +942,7 @@ static struct vfsmount *hugetlbfs_vfsmou
    >
    > static int can_do_hugetlb_shm(void)
    > {
    > - return likely(capable(CAP_IPC_LOCK) ||
    > - in_group_p(sysctl_hugetlb_shm_group) ||
    > - can_do_mlock());
    > + return (capable(CAP_IPC_LOCK) || in_group_p(sysctl_hugetlb_shm_group));
    > }
    >

    checkpatch complains about the () around the check being unnecessary.
    Not a big issue though.

    > struct file *hugetlb_file_setup(const char *name, size_t size)
    > @@ -962,9 +960,6 @@ struct file *hugetlb_file_setup(const ch
    > if (!can_do_hugetlb_shm())
    > return ERR_PTR(-EPERM);
    >
    > - if (!user_shm_lock(size, user))
    > - return ERR_PTR(-ENOMEM);
    > -
    > root = hugetlbfs_vfsmount->mnt_root;
    > quick_string.name = name;
    > quick_string.len = strlen(quick_string.name);
    > @@ -1002,7 +997,6 @@ out_inode:
    > out_dentry:
    > dput(dentry);
    > out_shm_unlock:
    > - user_shm_unlock(size, user);
    > return ERR_PTR(error);
    > }
    >

    Reviewed-by: Mel Gorman <mel@csn.ul.ie>

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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