linux-kernel - [patch 2/2] mm: Reintroduce and deprecate rlimit based access for SHM

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Date:	Fri, 20 Feb 2009 17:57:48 -0800
From:	Ravikiran G Thirumalai <kiran@...lex86.org>
To:	akpm@...ux-foundation.org
Cc:	wli@...ementarian.org, mel@....ul.ie, linux-mm@...ck.org,
	shai@...lex86.org, linux-kernel@...r.kernel.org
Subject: [patch 2/2] mm: Reintroduce and deprecate rlimit based access for
	SHM_HUGETLB 

Allow non root users with sufficient mlock rlimits to be able to allocate
hugetlb backed shm for now.  Deprecate this though.  This is being
deprecated because the mlock based rlimit checks for SHM_HUGETLB
is not consistent with mmap based huge page allocations.

Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
Cc: Mel Gorman <mel@....ul.ie>
Cc: Wli <wli@...ementarian.org>

Index: linux-2.6-tip/fs/hugetlbfs/inode.c
===================================================================
--- linux-2.6-tip.orig/fs/hugetlbfs/inode.c	2009-02-10 13:30:05.000000000 -0800
+++ linux-2.6-tip/fs/hugetlbfs/inode.c	2009-02-11 21:58:23.000000000 -0800
@@ -948,6 +948,7 @@ static int can_do_hugetlb_shm(void)
 struct file *hugetlb_file_setup(const char *name, size_t size)
 {
 	int error = -ENOMEM;
+	int unlock_shm = 0;
 	struct file *file;
 	struct inode *inode;
 	struct dentry *dentry, *root;
@@ -957,8 +958,14 @@ struct file *hugetlb_file_setup(const ch
 	if (!hugetlbfs_vfsmount)
 		return ERR_PTR(-ENOENT);
 
-	if (!can_do_hugetlb_shm())
-		return ERR_PTR(-EPERM);
+	if (!can_do_hugetlb_shm()) {
+		if (user_shm_lock(size, user)) {
+			unlock_shm = 1;
+			WARN_ONCE(1,
+			  "Using mlock ulimits for SHM_HUGETLB deprecated\n");
+		} else
+			return ERR_PTR(-EPERM);
+	}
 
 	root = hugetlbfs_vfsmount->mnt_root;
 	quick_string.name = name;
@@ -997,6 +1004,8 @@ out_inode:
 out_dentry:
 	dput(dentry);
 out_shm_unlock:
+	if (unlock_shm)
+		user_shm_unlock(size, user);
 	return ERR_PTR(error);
 }
 
Index: linux-2.6-tip/Documentation/feature-removal-schedule.txt
===================================================================
--- linux-2.6-tip.orig/Documentation/feature-removal-schedule.txt	2009-02-09 16:45:47.000000000 -0800
+++ linux-2.6-tip/Documentation/feature-removal-schedule.txt	2009-02-11 21:35:28.000000000 -0800
@@ -335,3 +335,14 @@ Why:	In 2.6.18 the Secmark concept was i
 	Secmark, it is time to deprecate the older mechanism and start the
 	process of removing the old code.
 Who:	Paul Moore <paul.moore@...com>
+---------------------------
+
+What:	Ability for non root users to shm_get hugetlb pages based on mlock
+	resource limits
+When:	2.6.31
+Why:	Non root users need to be part of /proc/sys/vm/hugetlb_shm_group or
+	have CAP_IPC_LOCK to be able to allocate shm segments backed by
+	huge pages.  The mlock based rlimit check to allow shm hugetlb is
+	inconsistent with mmap based allocations.  Hence it is being
+	deprecated.
+Who:	Ravikiran Thirumalai <kiran@...lex86.org>
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