[PATCH 3.16 091/114] xfs: introduce mmap/truncate lock

From: Ben Hutchings
Date: Mon Jun 13 2016 - 14:47:32 EST

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3.16.36-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Dave Chinner <dchinner@xxxxxxxxxx>

commit 653c60b633a9019a54a80d64b5ed33ecb214823c upstream.

Right now we cannot serialise mmap against truncate or hole punch
sanely. ->page_mkwrite is not able to take locks that the read IO
path normally takes (i.e. the inode iolock) because that could
result in lock inversions (read - iolock - page fault - page_mkwrite
- iolock) and so we cannot use an IO path lock to serialise page
write faults against truncate operations.

Instead, introduce a new lock that is used *only* in the
->page_mkwrite path that is the equivalent of the iolock. The lock
ordering in a page fault is i_mmaplock -> page lock -> i_ilock,
and so in truncate we can i_iolock -> i_mmaplock and so lock out
new write faults during the process of truncation.

Because i_mmap_lock is outside the page lock, we can hold it across
all the same operations we hold the i_iolock for. The only
difference is that we never hold the i_mmaplock in the normal IO
path and so do not ever have the possibility that we can page fault
inside it. Hence there are no recursion issues on the i_mmap_lock
and so we can use it to serialise page fault IO against inode
modification operations that affect the IO path.

This patch introduces the i_mmaplock infrastructure, lockdep
annotations and initialisation/destruction code. Use of the new lock
will be in subsequent patches.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: xfs@xxxxxxxxxxx
---
fs/xfs/xfs_inode.c | 128 ++++++++++++++++++++++++++++++++++++++++-------------
fs/xfs/xfs_inode.h | 29 +++++++++---
fs/xfs/xfs_super.c | 2 +
3 files changed, 121 insertions(+), 38 deletions(-)

--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -119,24 +119,34 @@ xfs_ilock_attr_map_shared(
}

/*
- * The xfs inode contains 2 locks: a multi-reader lock called the
- * i_iolock and a multi-reader lock called the i_lock. This routine
- * allows either or both of the locks to be obtained.
+ * The xfs inode contains 3 multi-reader locks: the i_iolock the i_mmap_lock and
+ * the i_lock. This routine allows various combinations of the locks to be
+ * obtained.
*
- * The 2 locks should always be ordered so that the IO lock is
- * obtained first in order to prevent deadlock.
+ * The 3 locks should always be ordered so that the IO lock is obtained first,
+ * the mmap lock second and the ilock last in order to prevent deadlock.
*
- * ip -- the inode being locked
- * lock_flags -- this parameter indicates the inode's locks
- * to be locked. It can be:
- * XFS_IOLOCK_SHARED,
- * XFS_IOLOCK_EXCL,
- * XFS_ILOCK_SHARED,
- * XFS_ILOCK_EXCL,
- * XFS_IOLOCK_SHARED | XFS_ILOCK_SHARED,
- * XFS_IOLOCK_SHARED | XFS_ILOCK_EXCL,
- * XFS_IOLOCK_EXCL | XFS_ILOCK_SHARED,
- * XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL
+ * Basic locking order:
+ *
+ * i_iolock -> i_mmap_lock -> page_lock -> i_ilock
+ *
+ * mmap_sem locking order:
+ *
+ * i_iolock -> page lock -> mmap_sem
+ * mmap_sem -> i_mmap_lock -> page_lock
+ *
+ * The difference in mmap_sem locking order mean that we cannot hold the
+ * i_mmap_lock over syscall based read(2)/write(2) based IO. These IO paths can
+ * fault in pages during copy in/out (for buffered IO) or require the mmap_sem
+ * in get_user_pages() to map the user pages into the kernel address space for
+ * direct IO. Similarly the i_iolock cannot be taken inside a page fault because
+ * page faults already hold the mmap_sem.
+ *
+ * Hence to serialise fully against both syscall and mmap based IO, we need to
+ * take both the i_iolock and the i_mmap_lock. These locks should *only* be both
+ * taken in places where we need to invalidate the page cache in a race
+ * free manner (e.g. truncate, hole punch and other extent manipulation
+ * functions).
*/
void
xfs_ilock(
@@ -152,6 +162,8 @@ xfs_ilock(
*/
ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
(XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
+ ASSERT((lock_flags & (XFS_MMAPLOCK_SHARED | XFS_MMAPLOCK_EXCL)) !=
+ (XFS_MMAPLOCK_SHARED | XFS_MMAPLOCK_EXCL));
ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
(XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_DEP_MASK)) == 0);
@@ -161,6 +173,11 @@ xfs_ilock(
else if (lock_flags & XFS_IOLOCK_SHARED)
mraccess_nested(&ip->i_iolock, XFS_IOLOCK_DEP(lock_flags));

+ if (lock_flags & XFS_MMAPLOCK_EXCL)
+ mrupdate_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
+ else if (lock_flags & XFS_MMAPLOCK_SHARED)
+ mraccess_nested(&ip->i_mmaplock, XFS_MMAPLOCK_DEP(lock_flags));
+
if (lock_flags & XFS_ILOCK_EXCL)
mrupdate_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
else if (lock_flags & XFS_ILOCK_SHARED)
@@ -193,6 +210,8 @@ xfs_ilock_nowait(
*/
ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
(XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
+ ASSERT((lock_flags & (XFS_MMAPLOCK_SHARED | XFS_MMAPLOCK_EXCL)) !=
+ (XFS_MMAPLOCK_SHARED | XFS_MMAPLOCK_EXCL));
ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
(XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_DEP_MASK)) == 0);
@@ -204,21 +223,35 @@ xfs_ilock_nowait(
if (!mrtryaccess(&ip->i_iolock))
goto out;
}
+
+ if (lock_flags & XFS_MMAPLOCK_EXCL) {
+ if (!mrtryupdate(&ip->i_mmaplock))
+ goto out_undo_iolock;
+ } else if (lock_flags & XFS_MMAPLOCK_SHARED) {
+ if (!mrtryaccess(&ip->i_mmaplock))
+ goto out_undo_iolock;
+ }
+
if (lock_flags & XFS_ILOCK_EXCL) {
if (!mrtryupdate(&ip->i_lock))
- goto out_undo_iolock;
+ goto out_undo_mmaplock;
} else if (lock_flags & XFS_ILOCK_SHARED) {
if (!mrtryaccess(&ip->i_lock))
- goto out_undo_iolock;
+ goto out_undo_mmaplock;
}
return 1;

- out_undo_iolock:
+out_undo_mmaplock:
+ if (lock_flags & XFS_MMAPLOCK_EXCL)
+ mrunlock_excl(&ip->i_mmaplock);
+ else if (lock_flags & XFS_MMAPLOCK_SHARED)
+ mrunlock_shared(&ip->i_mmaplock);
+out_undo_iolock:
if (lock_flags & XFS_IOLOCK_EXCL)
mrunlock_excl(&ip->i_iolock);
else if (lock_flags & XFS_IOLOCK_SHARED)
mrunlock_shared(&ip->i_iolock);
- out:
+out:
return 0;
}

@@ -246,6 +279,8 @@ xfs_iunlock(
*/
ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
(XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
+ ASSERT((lock_flags & (XFS_MMAPLOCK_SHARED | XFS_MMAPLOCK_EXCL)) !=
+ (XFS_MMAPLOCK_SHARED | XFS_MMAPLOCK_EXCL));
ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
(XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_DEP_MASK)) == 0);
@@ -256,6 +291,11 @@ xfs_iunlock(
else if (lock_flags & XFS_IOLOCK_SHARED)
mrunlock_shared(&ip->i_iolock);

+ if (lock_flags & XFS_MMAPLOCK_EXCL)
+ mrunlock_excl(&ip->i_mmaplock);
+ else if (lock_flags & XFS_MMAPLOCK_SHARED)
+ mrunlock_shared(&ip->i_mmaplock);
+
if (lock_flags & XFS_ILOCK_EXCL)
mrunlock_excl(&ip->i_lock);
else if (lock_flags & XFS_ILOCK_SHARED)
@@ -273,11 +313,14 @@ xfs_ilock_demote(
xfs_inode_t *ip,
uint lock_flags)
{
- ASSERT(lock_flags & (XFS_IOLOCK_EXCL|XFS_ILOCK_EXCL));
- ASSERT((lock_flags & ~(XFS_IOLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);
+ ASSERT(lock_flags & (XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL));
+ ASSERT((lock_flags &
+ ~(XFS_IOLOCK_EXCL|XFS_MMAPLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);

if (lock_flags & XFS_ILOCK_EXCL)
mrdemote(&ip->i_lock);
+ if (lock_flags & XFS_MMAPLOCK_EXCL)
+ mrdemote(&ip->i_mmaplock);
if (lock_flags & XFS_IOLOCK_EXCL)
mrdemote(&ip->i_iolock);

@@ -296,6 +339,12 @@ xfs_isilocked(
return rwsem_is_locked(&ip->i_lock.mr_lock);
}

+ if (lock_flags & (XFS_MMAPLOCK_EXCL|XFS_MMAPLOCK_SHARED)) {
+ if (!(lock_flags & XFS_MMAPLOCK_SHARED))
+ return !!ip->i_mmaplock.mr_writer;
+ return rwsem_is_locked(&ip->i_mmaplock.mr_lock);
+ }
+
if (lock_flags & (XFS_IOLOCK_EXCL|XFS_IOLOCK_SHARED)) {
if (!(lock_flags & XFS_IOLOCK_SHARED))
return !!ip->i_iolock.mr_writer;
@@ -316,14 +365,27 @@ int xfs_lock_delays;
#endif

/*
- * Bump the subclass so xfs_lock_inodes() acquires each lock with
- * a different value
+ * Bump the subclass so xfs_lock_inodes() acquires each lock with a different
+ * value. This shouldn't be called for page fault locking, but we also need to
+ * ensure we don't overrun the number of lockdep subclasses for the iolock or
+ * mmaplock as that is limited to 12 by the mmap lock lockdep annotations.
*/
static inline int
xfs_lock_inumorder(int lock_mode, int subclass)
{
- if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL))
+ if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL)) {
+ ASSERT(subclass + XFS_LOCK_INUMORDER <
+ (1 << (XFS_MMAPLOCK_SHIFT - XFS_IOLOCK_SHIFT)));
lock_mode |= (subclass + XFS_LOCK_INUMORDER) << XFS_IOLOCK_SHIFT;
+ }
+
+ if (lock_mode & (XFS_MMAPLOCK_SHARED|XFS_MMAPLOCK_EXCL)) {
+ ASSERT(subclass + XFS_LOCK_INUMORDER <
+ (1 << (XFS_ILOCK_SHIFT - XFS_MMAPLOCK_SHIFT)));
+ lock_mode |= (subclass + XFS_LOCK_INUMORDER) <<
+ XFS_MMAPLOCK_SHIFT;
+ }
+
if (lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL))
lock_mode |= (subclass + XFS_LOCK_INUMORDER) << XFS_ILOCK_SHIFT;

@@ -442,10 +504,10 @@ again:
}

/*
- * xfs_lock_two_inodes() can only be used to lock one type of lock
- * at a time - the iolock or the ilock, but not both at once. If
- * we lock both at once, lockdep will report false positives saying
- * we have violated locking orders.
+ * xfs_lock_two_inodes() can only be used to lock one type of lock at a time -
+ * the iolock, the mmaplock or the ilock, but not more than one at a time. If we
+ * lock more than one at a time, lockdep will report false positives saying we
+ * have violated locking orders.
*/
void
xfs_lock_two_inodes(
@@ -457,8 +519,12 @@ xfs_lock_two_inodes(
int attempts = 0;
xfs_log_item_t *lp;

- if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL))
- ASSERT((lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)) == 0);
+ if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL)) {
+ ASSERT(!(lock_mode & (XFS_MMAPLOCK_SHARED|XFS_MMAPLOCK_EXCL)));
+ ASSERT(!(lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)));
+ } else if (lock_mode & (XFS_MMAPLOCK_SHARED|XFS_MMAPLOCK_EXCL))
+ ASSERT(!(lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL)));
+
ASSERT(ip0->i_ino != ip1->i_ino);

if (ip0->i_ino > ip1->i_ino) {
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -57,6 +57,7 @@ typedef struct xfs_inode {
struct xfs_inode_log_item *i_itemp; /* logging information */
mrlock_t i_lock; /* inode lock */
mrlock_t i_iolock; /* inode IO lock */
+ mrlock_t i_mmaplock; /* inode mmap IO lock */
atomic_t i_pincount; /* inode pin count */
spinlock_t i_flags_lock; /* inode i_flags lock */
/* Miscellaneous state. */
@@ -264,15 +265,20 @@ static inline int xfs_isiflocked(struct
#define XFS_IOLOCK_SHARED (1<<1)
#define XFS_ILOCK_EXCL (1<<2)
#define XFS_ILOCK_SHARED (1<<3)
+#define XFS_MMAPLOCK_EXCL (1<<4)
+#define XFS_MMAPLOCK_SHARED (1<<5)

#define XFS_LOCK_MASK (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED \
- | XFS_ILOCK_EXCL | XFS_ILOCK_SHARED)
+ | XFS_ILOCK_EXCL | XFS_ILOCK_SHARED \
+ | XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)

#define XFS_LOCK_FLAGS \
{ XFS_IOLOCK_EXCL, "IOLOCK_EXCL" }, \
{ XFS_IOLOCK_SHARED, "IOLOCK_SHARED" }, \
{ XFS_ILOCK_EXCL, "ILOCK_EXCL" }, \
- { XFS_ILOCK_SHARED, "ILOCK_SHARED" }
+ { XFS_ILOCK_SHARED, "ILOCK_SHARED" }, \
+ { XFS_MMAPLOCK_EXCL, "MMAPLOCK_EXCL" }, \
+ { XFS_MMAPLOCK_SHARED, "MMAPLOCK_SHARED" }

/*
@@ -303,17 +309,26 @@ static inline int xfs_isiflocked(struct
#define XFS_IOLOCK_SHIFT 16
#define XFS_IOLOCK_PARENT (XFS_LOCK_PARENT << XFS_IOLOCK_SHIFT)

+#define XFS_MMAPLOCK_SHIFT 20
+
#define XFS_ILOCK_SHIFT 24
#define XFS_ILOCK_PARENT (XFS_LOCK_PARENT << XFS_ILOCK_SHIFT)
#define XFS_ILOCK_RTBITMAP (XFS_LOCK_RTBITMAP << XFS_ILOCK_SHIFT)
#define XFS_ILOCK_RTSUM (XFS_LOCK_RTSUM << XFS_ILOCK_SHIFT)

-#define XFS_IOLOCK_DEP_MASK 0x00ff0000
+#define XFS_IOLOCK_DEP_MASK 0x000f0000
+#define XFS_MMAPLOCK_DEP_MASK 0x00f00000
#define XFS_ILOCK_DEP_MASK 0xff000000
-#define XFS_LOCK_DEP_MASK (XFS_IOLOCK_DEP_MASK | XFS_ILOCK_DEP_MASK)
-
-#define XFS_IOLOCK_DEP(flags) (((flags) & XFS_IOLOCK_DEP_MASK) >> XFS_IOLOCK_SHIFT)
-#define XFS_ILOCK_DEP(flags) (((flags) & XFS_ILOCK_DEP_MASK) >> XFS_ILOCK_SHIFT)
+#define XFS_LOCK_DEP_MASK (XFS_IOLOCK_DEP_MASK | \
+ XFS_MMAPLOCK_DEP_MASK | \
+ XFS_ILOCK_DEP_MASK)
+
+#define XFS_IOLOCK_DEP(flags) (((flags) & XFS_IOLOCK_DEP_MASK) \
+ >> XFS_IOLOCK_SHIFT)
+#define XFS_MMAPLOCK_DEP(flags) (((flags) & XFS_MMAPLOCK_DEP_MASK) \
+ >> XFS_MMAPLOCK_SHIFT)
+#define XFS_ILOCK_DEP(flags) (((flags) & XFS_ILOCK_DEP_MASK) \
+ >> XFS_ILOCK_SHIFT)

/*
* For multiple groups support: if S_ISGID bit is set in the parent
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -982,6 +982,8 @@ xfs_fs_inode_init_once(
atomic_set(&ip->i_pincount, 0);
spin_lock_init(&ip->i_flags_lock);

+ mrlock_init(&ip->i_mmaplock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
+ "xfsino", ip->i_ino);
mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
"xfsino", ip->i_ino);
}

Next message: Ben Hutchings: "[PATCH 3.16 053/114] workqueue: fix ghost PENDING flag while doing MQ IO"
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