Merge branch 'locks' of git://linux-nfs.org/~bfields/linux

* 'locks' of git://linux-nfs.org/~bfields/linux: nfsd: remove IS_ISMNDLCK macro Rework /proc/locks via seq_files and seq_list helpers fs/locks.c: use list_for_each_entry() instead of list_for_each() NFS: clean up explicit check for mandatory locks AFS: clean up explicit check for mandatory locks 9PFS: clean up explicit check for mandatory locks GFS2: clean up explicit check for mandatory locks Cleanup macros for distinguishing mandatory locks Documentation: move locks.txt in filesystems/ locks: add warning about mandatory locking races Documentation: move mandatory locking documentation to filesystems/ locks: Fix potential OOPS in generic_setlease() Use list_first_entry in locks_wake_up_blocks locks: fix flock_lock_file() comment Memory shortage can result in inconsistent flocks state locks: kill redundant local variable locks: reverse order of posix_locks_conflict() arguments
2007-10-15 16:07:40 -07:00 · 2007-10-15 16:07:40 -07:00 · 541010e4b8
commit 541010e4b8
parent e457f790d8 5e7fc43642
14 changed files with 158 additions and 147 deletions
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@ -145,7 +145,7 @@ fb/
 feature-removal-schedule.txt
 	- list of files and features that are going to be removed.
 filesystems/
-	- directory with info on the various filesystems that Linux supports.
+	- info on the vfs and the various filesystems that Linux supports.
 firmware_class/
 	- request_firmware() hotplug interface info.
 floppy.txt
@ -230,8 +230,6 @@ local_ops.txt
 	- semantics and behavior of local atomic operations.
 lockdep-design.txt
 	- documentation on the runtime locking correctness validator.
-locks.txt
-	- info on file locking implementations, flock() vs. fcntl(), etc.
 logo.gif
 	- full colour GIF image of Linux logo (penguin - Tux).
 logo.txt
@ -240,8 +238,6 @@ m68k/
 	- directory with info about Linux on Motorola 68k architecture.
 magic-number.txt
 	- list of magic numbers used to mark/protect kernel data structures.
-mandatory.txt
-	- info on the Linux implementation of Sys V mandatory file locking.
 mca.txt
 	- info on supporting Micro Channel Architecture (e.g. PS/2) systems.
 md.txt
--- a/Documentation/filesystems/00-INDEX
+++ b/Documentation/filesystems/00-INDEX
@ -52,6 +52,10 @@ isofs.txt
 	- info and mount options for the ISO 9660 (CDROM) filesystem.
 jfs.txt
 	- info and mount options for the JFS filesystem.
+locks.txt
+	- info on file locking implementations, flock() vs. fcntl(), etc.
+mandatory-locking.txt
+	- info on the Linux implementation of Sys V mandatory file locking.
 ncpfs.txt
 	- info on Novell Netware(tm) filesystem using NCP protocol.
 ntfs.txt
--- a/Documentation/filesystems/locks.txt
+++ b/Documentation/filesystems/locks.txt
@ -53,11 +53,11 @@ fcntl(), with all the problems that implies.
 1.3 Mandatory Locking As A Mount Option
 ---------------------------------------

-Mandatory locking, as described in 'Documentation/mandatory.txt' was prior
-to this release a general configuration option that was valid for all
-mounted filesystems. This had a number of inherent dangers, not the least
-of which was the ability to freeze an NFS server by asking it to read a
-file for which a mandatory lock existed.
+Mandatory locking, as described in 'Documentation/filesystems/mandatory.txt'
+was prior to this release a general configuration option that was valid for
+all mounted filesystems.  This had a number of inherent dangers, not the
+least of which was the ability to freeze an NFS server by asking it to read
+a file for which a mandatory lock existed.

 From this release of the kernel, mandatory locking can be turned on and off
 on a per-filesystem basis, using the mount options 'mand' and 'nomand'.
--- a/Documentation/filesystems/mandatory-locking.txt
+++ b/Documentation/filesystems/mandatory-locking.txt
@ -3,7 +3,26 @@
 		Andy Walker <andy@lysaker.kvaerner.no>

 			   15 April 1996
+		     (Updated September 2007)

+0. Why you should avoid mandatory locking
+-----------------------------------------
+
+The Linux implementation is prey to a number of difficult-to-fix race
+conditions which in practice make it not dependable:
+
+	- The write system call checks for a mandatory lock only once
+	  at its start.  It is therefore possible for a lock request to
+	  be granted after this check but before the data is modified.
+	  A process may then see file data change even while a mandatory
+	  lock was held.
+	- Similarly, an exclusive lock may be granted on a file after
+	  the kernel has decided to proceed with a read, but before the
+	  read has actually completed, and the reading process may see
+	  the file data in a state which should not have been visible
+	  to it.
+	- Similar races make the claimed mutual exclusion between lock
+	  and mmap similarly unreliable.

 1. What is  mandatory locking?
 ------------------------------
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@ -105,7 +105,7 @@ static int v9fs_file_lock(struct file *filp, int cmd, struct file_lock *fl)
 	P9_DPRINTK(P9_DEBUG_VFS, "filp: %p lock: %p\n", filp, fl);

 	/* No mandatory locks */
-	if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+	if (__mandatory_lock(inode))
 		return -ENOLCK;

 	if ((IS_SETLK(cmd) || IS_SETLKW(cmd)) && fl->fl_type != F_UNLCK) {
--- a/fs/afs/flock.c
+++ b/fs/afs/flock.c
@ -524,8 +524,7 @@ int afs_lock(struct file *file, int cmd, struct file_lock *fl)
 	       (long long) fl->fl_start, (long long) fl->fl_end);

 	/* AFS doesn't support mandatory locks */
-	if ((vnode->vfs_inode.i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
-	    fl->fl_type != F_UNLCK)
+	if (__mandatory_lock(&vnode->vfs_inode) && fl->fl_type != F_UNLCK)
 		return -ENOLCK;

 	if (IS_GETLK(cmd))
--- a/fs/gfs2/ops_file.c
+++ b/fs/gfs2/ops_file.c
@ -535,7 +535,7 @@ static int gfs2_lock(struct file *file, int cmd, struct file_lock *fl)

 	if (!(fl->fl_flags & FL_POSIX))
 		return -ENOLCK;
-	if ((ip->i_inode.i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+	if (__mandatory_lock(&ip->i_inode))
 		return -ENOLCK;

 	if (sdp->sd_args.ar_localflocks) {
@ -636,7 +636,7 @@ static int gfs2_flock(struct file *file, int cmd, struct file_lock *fl)

 	if (!(fl->fl_flags & FL_FLOCK))
 		return -ENOLCK;
-	if ((ip->i_inode.i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+	if (__mandatory_lock(&ip->i_inode))
 		return -ENOLCK;

 	if (sdp->sd_args.ar_localflocks)
--- a/fs/locks.c
+++ b/fs/locks.c
@ -534,7 +534,9 @@ static void locks_insert_block(struct file_lock *blocker,
 static void locks_wake_up_blocks(struct file_lock *blocker)
 {
 	while (!list_empty(&blocker->fl_block)) {
-		struct file_lock *waiter = list_entry(blocker->fl_block.next,
+		struct file_lock *waiter;
+
+		waiter = list_first_entry(&blocker->fl_block,
 				struct file_lock, fl_block);
 		__locks_delete_block(waiter);
 		if (waiter->fl_lmops && waiter->fl_lmops->fl_notify)
@ -668,7 +670,7 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
 	for (cfl = filp->f_path.dentry->d_inode->i_flock; cfl; cfl = cfl->fl_next) {
 		if (!IS_POSIX(cfl))
 			continue;
-		if (posix_locks_conflict(cfl, fl))
+		if (posix_locks_conflict(fl, cfl))
 			break;
 	}
 	if (cfl)
@ -698,13 +700,12 @@ EXPORT_SYMBOL(posix_test_lock);
 static int posix_locks_deadlock(struct file_lock *caller_fl,
 				struct file_lock *block_fl)
 {
-	struct list_head *tmp;
+	struct file_lock *fl;

 next_task:
 	if (posix_same_owner(caller_fl, block_fl))
 		return 1;
-	list_for_each(tmp, &blocked_list) {
-		struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
+	list_for_each_entry(fl, &blocked_list, fl_link) {
 		if (posix_same_owner(fl, block_fl)) {
 			fl = fl->fl_next;
 			block_fl = fl;
@ -715,8 +716,7 @@ static int posix_locks_deadlock(struct file_lock *caller_fl,
 }

 /* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
- * at the head of the list, but that's secret knowledge known only to
- * flock_lock_file and posix_lock_file.
+ * after any leases, but before any posix locks.
 *
 * Note that if called with an FL_EXISTS argument, the caller may determine
 * whether or not a lock was successfully freed by testing the return
@ -733,6 +733,15 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
 	lock_kernel();
 	if (request->fl_flags & FL_ACCESS)
 		goto find_conflict;
+
+	if (request->fl_type != F_UNLCK) {
+		error = -ENOMEM;
+		new_fl = locks_alloc_lock();
+		if (new_fl == NULL)
+			goto out;
+		error = 0;
+	}
+
 	for_each_lock(inode, before) {
 		struct file_lock *fl = *before;
 		if (IS_POSIX(fl))
@ -754,10 +763,6 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
 		goto out;
 	}

-	error = -ENOMEM;
-	new_fl = locks_alloc_lock();
-	if (new_fl == NULL)
-		goto out;
 	/*
 	 * If a higher-priority process was blocked on the old file lock,
 	 * give it the opportunity to lock the file.
@ -819,7 +824,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
 	lock_kernel();
 	if (request->fl_type != F_UNLCK) {
 		for_each_lock(inode, before) {
-			struct file_lock *fl = *before;
+			fl = *before;
 			if (!IS_POSIX(fl))
 				continue;
 			if (!posix_locks_conflict(request, fl))
@ -1113,7 +1118,7 @@ int locks_mandatory_area(int read_write, struct inode *inode,
 			 * If we've been sleeping someone might have
 			 * changed the permissions behind our back.
 			 */
-			if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+			if (__mandatory_lock(inode))
 				continue;
 		}

@ -1337,6 +1342,7 @@ int fcntl_getlease(struct file *filp)
 int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
 {
 	struct file_lock *fl, **before, **my_before = NULL, *lease;
+	struct file_lock *new_fl = NULL;
 	struct dentry *dentry = filp->f_path.dentry;
 	struct inode *inode = dentry->d_inode;
 	int error, rdlease_count = 0, wrlease_count = 0;
@ -1363,6 +1369,11 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
 		|| (atomic_read(&inode->i_count) > 1)))
 		goto out;

+	error = -ENOMEM;
+	new_fl = locks_alloc_lock();
+	if (new_fl == NULL)
+		goto out;
+
 	/*
 	 * At this point, we know that if there is an exclusive
 	 * lease on this file, then we hold it on this filp
@ -1405,18 +1416,15 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
 	if (!leases_enable)
 		goto out;

-	error = -ENOMEM;
-	fl = locks_alloc_lock();
-	if (fl == NULL)
-		goto out;
+	locks_copy_lock(new_fl, lease);
+	locks_insert_lock(before, new_fl);

-	locks_copy_lock(fl, lease);
+	*flp = new_fl;
+	return 0;

-	locks_insert_lock(before, fl);
-
-	*flp = fl;
-	error = 0;
 out:
+	if (new_fl != NULL)
+		locks_free_lock(new_fl);
 	return error;
 }
 EXPORT_SYMBOL(generic_setlease);
@ -1752,9 +1760,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
 	/* Don't allow mandatory locks on files that may be memory mapped
 	 * and shared.
 	 */
-	if (IS_MANDLOCK(inode) &&
-	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
-	    mapping_writably_mapped(filp->f_mapping)) {
+	if (mandatory_lock(inode) && mapping_writably_mapped(filp->f_mapping)) {
 		error = -EAGAIN;
 		goto out;
 	}
@ -1878,9 +1884,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
 	/* Don't allow mandatory locks on files that may be memory mapped
 	 * and shared.
 	 */
-	if (IS_MANDLOCK(inode) &&
-	    (inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
-	    mapping_writably_mapped(filp->f_mapping)) {
+	if (mandatory_lock(inode) && mapping_writably_mapped(filp->f_mapping)) {
 		error = -EAGAIN;
 		goto out;
 	}
@ -2062,138 +2066,114 @@ int vfs_cancel_lock(struct file *filp, struct file_lock *fl)

 EXPORT_SYMBOL_GPL(vfs_cancel_lock);

-static void lock_get_status(char* out, struct file_lock *fl, int id, char *pfx)
+#ifdef CONFIG_PROC_FS
+#include <linux/seq_file.h>
+
+static void lock_get_status(struct seq_file *f, struct file_lock *fl,
+							int id, char *pfx)
 {
 	struct inode *inode = NULL;

 	if (fl->fl_file != NULL)
 		inode = fl->fl_file->f_path.dentry->d_inode;

-	out += sprintf(out, "%d:%s ", id, pfx);
+	seq_printf(f, "%d:%s ", id, pfx);
 	if (IS_POSIX(fl)) {
-		out += sprintf(out, "%6s %s ",
+		seq_printf(f, "%6s %s ",
 			     (fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
 			     (inode == NULL) ? "*NOINODE*" :
-			     (IS_MANDLOCK(inode) &&
-			      (inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
-			     "MANDATORY" : "ADVISORY ");
+			     mandatory_lock(inode) ? "MANDATORY" : "ADVISORY ");
 	} else if (IS_FLOCK(fl)) {
 		if (fl->fl_type & LOCK_MAND) {
-			out += sprintf(out, "FLOCK  MSNFS     ");
+			seq_printf(f, "FLOCK  MSNFS     ");
 		} else {
-			out += sprintf(out, "FLOCK  ADVISORY  ");
+			seq_printf(f, "FLOCK  ADVISORY  ");
 		}
 	} else if (IS_LEASE(fl)) {
-		out += sprintf(out, "LEASE  ");
+		seq_printf(f, "LEASE  ");
 		if (fl->fl_type & F_INPROGRESS)
-			out += sprintf(out, "BREAKING  ");
+			seq_printf(f, "BREAKING  ");
 		else if (fl->fl_file)
-			out += sprintf(out, "ACTIVE    ");
+			seq_printf(f, "ACTIVE    ");
 		else
-			out += sprintf(out, "BREAKER   ");
+			seq_printf(f, "BREAKER   ");
 	} else {
-		out += sprintf(out, "UNKNOWN UNKNOWN  ");
+		seq_printf(f, "UNKNOWN UNKNOWN  ");
 	}
 	if (fl->fl_type & LOCK_MAND) {
-		out += sprintf(out, "%s ",
+		seq_printf(f, "%s ",
 			       (fl->fl_type & LOCK_READ)
 			       ? (fl->fl_type & LOCK_WRITE) ? "RW   " : "READ "
 			       : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
 	} else {
-		out += sprintf(out, "%s ",
+		seq_printf(f, "%s ",
 			       (fl->fl_type & F_INPROGRESS)
 			       ? (fl->fl_type & F_UNLCK) ? "UNLCK" : "READ "
 			       : (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
 	}
 	if (inode) {
 #ifdef WE_CAN_BREAK_LSLK_NOW
-		out += sprintf(out, "%d %s:%ld ", fl->fl_pid,
+		seq_printf(f, "%d %s:%ld ", fl->fl_pid,
 				inode->i_sb->s_id, inode->i_ino);
 #else
 		/* userspace relies on this representation of dev_t ;-( */
-		out += sprintf(out, "%d %02x:%02x:%ld ", fl->fl_pid,
+		seq_printf(f, "%d %02x:%02x:%ld ", fl->fl_pid,
 				MAJOR(inode->i_sb->s_dev),
 				MINOR(inode->i_sb->s_dev), inode->i_ino);
 #endif
 	} else {
-		out += sprintf(out, "%d <none>:0 ", fl->fl_pid);
+		seq_printf(f, "%d <none>:0 ", fl->fl_pid);
 	}
 	if (IS_POSIX(fl)) {
 		if (fl->fl_end == OFFSET_MAX)
-			out += sprintf(out, "%Ld EOF\n", fl->fl_start);
+			seq_printf(f, "%Ld EOF\n", fl->fl_start);
 		else
-			out += sprintf(out, "%Ld %Ld\n", fl->fl_start,
-					fl->fl_end);
+			seq_printf(f, "%Ld %Ld\n", fl->fl_start, fl->fl_end);
 	} else {
-		out += sprintf(out, "0 EOF\n");
+		seq_printf(f, "0 EOF\n");
 	}
 }

-static void move_lock_status(char **p, off_t* pos, off_t offset)
+static int locks_show(struct seq_file *f, void *v)
 {
-	int len;
-	len = strlen(*p);
-	if(*pos >= offset) {
-		/* the complete line is valid */
-		*p += len;
-		*pos += len;
-		return;
-	}
-	if(*pos+len > offset) {
-		/* use the second part of the line */
-		int i = offset-*pos;
-		memmove(*p,*p+i,len-i);
-		*p += len-i;
-		*pos += len;
-		return;
-	}
-	/* discard the complete line */
-	*pos += len;
+	struct file_lock *fl, *bfl;
+
+	fl = list_entry(v, struct file_lock, fl_link);
+
+	lock_get_status(f, fl, (long)f->private, "");
+
+	list_for_each_entry(bfl, &fl->fl_block, fl_block)
+		lock_get_status(f, bfl, (long)f->private, " ->");
+
+	f->private++;
+	return 0;
 }

-/**
- *	get_locks_status	-	reports lock usage in /proc/locks
- *	@buffer: address in userspace to write into
- *	@start: ?
- *	@offset: how far we are through the buffer
- *	@length: how much to read
- */
-
-int get_locks_status(char *buffer, char **start, off_t offset, int length)
+static void *locks_start(struct seq_file *f, loff_t *pos)
 {
-	struct list_head *tmp;
-	char *q = buffer;
-	off_t pos = 0;
-	int i = 0;
-
 	lock_kernel();
-	list_for_each(tmp, &file_lock_list) {
-		struct list_head *btmp;
-		struct file_lock *fl = list_entry(tmp, struct file_lock, fl_link);
-		lock_get_status(q, fl, ++i, "");
-		move_lock_status(&q, &pos, offset);
-
-		if(pos >= offset+length)
-			goto done;
-
-		list_for_each(btmp, &fl->fl_block) {
-			struct file_lock *bfl = list_entry(btmp,
-					struct file_lock, fl_block);
-			lock_get_status(q, bfl, i, " ->");
-			move_lock_status(&q, &pos, offset);
-
-			if(pos >= offset+length)
-				goto done;
-		}
-	}
-done:
-	unlock_kernel();
-	*start = buffer;
-	if(q-buffer < length)
-		return (q-buffer);
-	return length;
+	f->private = (void *)1;
+	return seq_list_start(&file_lock_list, *pos);
 }

+static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
+{
+	return seq_list_next(v, &file_lock_list, pos);
+}
+
+static void locks_stop(struct seq_file *f, void *v)
+{
+	unlock_kernel();
+}
+
+struct seq_operations locks_seq_operations = {
+	.start	= locks_start,
+	.next	= locks_next,
+	.stop	= locks_stop,
+	.show	= locks_show,
+};
+#endif
+
 /**
 *	lock_may_read - checks that the region is free of locks
 *	@inode: the inode that is being read
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@ -577,8 +577,7 @@ static int nfs_lock(struct file *filp, int cmd, struct file_lock *fl)
 	nfs_inc_stats(inode, NFSIOS_VFSLOCK);

 	/* No mandatory locks over NFS */
-	if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
-	    fl->fl_type != F_UNLCK)
+	if (__mandatory_lock(inode) && fl->fl_type != F_UNLCK)
 		return -ENOLCK;

 	if (IS_GETLK(cmd))
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@ -2035,7 +2035,7 @@ static inline int
 io_during_grace_disallowed(struct inode *inode, int flags)
 {
 	return nfs4_in_grace() && (flags & (RD_STATE | WR_STATE))
-		&& MANDATORY_LOCK(inode);
+		&& mandatory_lock(inode);
 }

 /*
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@ -61,12 +61,6 @@
 #define NFSDDBG_FACILITY		NFSDDBG_FILEOP


-/* We must ignore files (but only files) which might have mandatory
- * locks on them because there is no way to know if the accesser has
- * the lock.
- */
-#define IS_ISMNDLK(i)	(S_ISREG((i)->i_mode) && MANDATORY_LOCK(i))
-
 /*
 * This is a cache of readahead params that help us choose the proper
 * readahead strategy. Initially, we set all readahead parameters to 0
@ -689,7 +683,12 @@ nfsd_open(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 	err = nfserr_perm;
 	if (IS_APPEND(inode) && (access & MAY_WRITE))
 		goto out;
-	if (IS_ISMNDLK(inode))
+	/*
+	 * We must ignore files (but only files) which might have mandatory
+	 * locks on them because there is no way to know if the accesser has
+	 * the lock.
+	 */
+	if (S_ISREG((inode)->i_mode) && mandatory_lock(inode))
 		goto out;

 	if (!inode->i_fop)
--- a/fs/proc/proc_misc.c
+++ b/fs/proc/proc_misc.c
@ -66,7 +66,6 @@ extern int get_stram_list(char *);
 extern int get_filesystem_list(char *);
 extern int get_exec_domain_list(char *);
 extern int get_dma_list(char *);
-extern int get_locks_status (char *, char **, off_t, int);

 static int proc_calc_metrics(char *page, char **start, off_t off,
 				 int count, int *eof, int len)
@ -624,16 +623,18 @@ static int cmdline_read_proc(char *page, char **start, off_t off,
 	return proc_calc_metrics(page, start, off, count, eof, len);
 }

-static int locks_read_proc(char *page, char **start, off_t off,
-				 int count, int *eof, void *data)
+static int locks_open(struct inode *inode, struct file *filp)
 {
-	int len = get_locks_status(page, start, off, count);
-
-	if (len < count)
-		*eof = 1;
-	return len;
+	return seq_open(filp, &locks_seq_operations);
 }

+static const struct file_operations proc_locks_operations = {
+	.open		= locks_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
 static int execdomains_read_proc(char *page, char **start, off_t off,
 				 int count, int *eof, void *data)
 {
@ -691,7 +692,6 @@ void __init proc_misc_init(void)
 #endif
 		{"filesystems",	filesystems_read_proc},
 		{"cmdline",	cmdline_read_proc},
-		{"locks",	locks_read_proc},
 		{"execdomains",	execdomains_read_proc},
 		{NULL,}
 	};
@ -709,6 +709,7 @@ void __init proc_misc_init(void)
 			entry->proc_fops = &proc_kmsg_operations;
 	}
 #endif
+	create_seq_entry("locks", 0, &proc_locks_operations);
 	create_seq_entry("devices", 0, &proc_devinfo_operations);
 	create_seq_entry("cpuinfo", 0, &proc_cpuinfo_operations);
 #ifdef CONFIG_BLOCK
--- a/fs/read_write.c
+++ b/fs/read_write.c
@ -205,7 +205,7 @@ int rw_verify_area(int read_write, struct file *file, loff_t *ppos, size_t count
 	if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
 		goto Einval;

-	if (unlikely(inode->i_flock && MANDATORY_LOCK(inode))) {
+	if (unlikely(inode->i_flock && mandatory_lock(inode))) {
 		int retval = locks_mandatory_area(
 			read_write == READ ? FLOCK_VERIFY_READ : FLOCK_VERIFY_WRITE,
 			inode, file, pos, count);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@ -883,6 +883,7 @@ extern int vfs_setlease(struct file *, long, struct file_lock **);
 extern int lease_modify(struct file_lock **, int);
 extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
 extern int lock_may_write(struct inode *, loff_t start, unsigned long count);
+extern struct seq_operations locks_seq_operations;

 struct fasync_struct {
 	int	magic;
@ -1375,12 +1376,25 @@ extern int locks_mandatory_area(int, struct inode *, struct file *, loff_t, size
 * Candidates for mandatory locking have the setgid bit set
 * but no group execute bit -  an otherwise meaningless combination.
 */
-#define MANDATORY_LOCK(inode) \
-	(IS_MANDLOCK(inode) && ((inode)->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
+
+static inline int __mandatory_lock(struct inode *ino)
+{
+	return (ino->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID;
+}
+
+/*
+ * ... and these candidates should be on MS_MANDLOCK mounted fs,
+ * otherwise these will be advisory locks
+ */
+
+static inline int mandatory_lock(struct inode *ino)
+{
+	return IS_MANDLOCK(ino) && __mandatory_lock(ino);
+}

 static inline int locks_verify_locked(struct inode *inode)
 {
-	if (MANDATORY_LOCK(inode))
+	if (mandatory_lock(inode))
 		return locks_mandatory_locked(inode);
 	return 0;
 }
@ -1391,7 +1405,7 @@ static inline int locks_verify_truncate(struct inode *inode,
 				    struct file *filp,
 				    loff_t size)
 {
-	if (inode->i_flock && MANDATORY_LOCK(inode))
+	if (inode->i_flock && mandatory_lock(inode))
 		return locks_mandatory_area(
 			FLOCK_VERIFY_WRITE, inode, filp,
 			size < inode->i_size ? size : inode->i_size,