[PATCH v7 04/12] fs: MAP_DIRECT core

[Dan Williams <dan.j.williams@intel.com>]

Introduce a set of helper apis for filesystems to establish FL_LAYOUT
leases to protect against writes and block map updates while a
MAP_DIRECT mapping is established. While the lease protects against the
syscall write path and fallocate it does not protect against allocating
write-faults, so this relies on i_mapdcount to disable block map updates
from write faults.

Like the pnfs case MAP_DIRECT does its own timeout of the lease since we
need to have a process context for running map_direct_invalidate().

Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Jeff Layton <jlayton@poochiereds.net>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/Makefile               |    2 
 fs/mapdirect.c            |  232 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mapdirect.h |   45 +++++++++
 3 files changed, 278 insertions(+), 1 deletion(-)
 create mode 100644 fs/mapdirect.c
 create mode 100644 include/linux/mapdirect.h

diff --git a/fs/Makefile b/fs/Makefile
index 7bbaca9c67b1..c0e791d235d8 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -29,7 +29,7 @@ obj-$(CONFIG_TIMERFD)		+= timerfd.o
 obj-$(CONFIG_EVENTFD)		+= eventfd.o
 obj-$(CONFIG_USERFAULTFD)	+= userfaultfd.o
 obj-$(CONFIG_AIO)               += aio.o
-obj-$(CONFIG_FS_DAX)		+= dax.o
+obj-$(CONFIG_FS_DAX)		+= dax.o mapdirect.o
 obj-$(CONFIG_FS_ENCRYPTION)	+= crypto/
 obj-$(CONFIG_FILE_LOCKING)      += locks.o
 obj-$(CONFIG_COMPAT)		+= compat.o compat_ioctl.o
diff --git a/fs/mapdirect.c b/fs/mapdirect.c
new file mode 100644
index 000000000000..9ac7c1d946a2
--- /dev/null
+++ b/fs/mapdirect.c
@@ -0,0 +1,232 @@
+/*
+ * Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/mapdirect.h>
+#include <linux/workqueue.h>
+#include <linux/signal.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+
+#define MAPDIRECT_BREAK 0
+#define MAPDIRECT_VALID 1
+
+struct map_direct_state {
+	atomic_t mds_ref;
+	atomic_t mds_vmaref;
+	unsigned long mds_state;
+	struct inode *mds_inode;
+	struct delayed_work mds_work;
+	struct fasync_struct *mds_fa;
+	struct vm_area_struct *mds_vma;
+};
+
+bool is_map_direct_valid(struct map_direct_state *mds)
+{
+	return test_bit(MAPDIRECT_VALID, &mds->mds_state);
+}
+EXPORT_SYMBOL_GPL(is_map_direct_valid);
+
+static void put_map_direct(struct map_direct_state *mds)
+{
+	if (!atomic_dec_and_test(&mds->mds_ref))
+		return;
+	kfree(mds);
+}
+
+int put_map_direct_vma(struct map_direct_state *mds)
+{
+	struct vm_area_struct *vma = mds->mds_vma;
+	struct file *file = vma->vm_file;
+	struct inode *inode = file_inode(file);
+	void *owner = mds;
+
+	if (!atomic_dec_and_test(&mds->mds_vmaref))
+		return 0;
+
+	/*
+	 * Flush in-flight+forced lm_break events that may be
+	 * referencing this dying vma.
+	 */
+	mds->mds_vma = NULL;
+	set_bit(MAPDIRECT_BREAK, &mds->mds_state);
+	vfs_setlease(vma->vm_file, F_UNLCK, NULL, &owner);
+	flush_delayed_work(&mds->mds_work);
+	iput(inode);
+
+	put_map_direct(mds);
+	return 1;
+}
+EXPORT_SYMBOL_GPL(put_map_direct_vma);
+
+void get_map_direct_vma(struct map_direct_state *mds)
+{
+	atomic_inc(&mds->mds_vmaref);
+}
+EXPORT_SYMBOL_GPL(get_map_direct_vma);
+
+static void map_direct_invalidate(struct work_struct *work)
+{
+	struct map_direct_state *mds;
+	struct vm_area_struct *vma;
+	struct inode *inode;
+	void *owner;
+
+	mds = container_of(work, typeof(*mds), mds_work.work);
+
+	clear_bit(MAPDIRECT_VALID, &mds->mds_state);
+
+	vma = ACCESS_ONCE(mds->mds_vma);
+	inode = mds->mds_inode;
+	if (vma) {
+		unsigned long len = vma->vm_end - vma->vm_start;
+		loff_t start = (loff_t) vma->vm_pgoff * PAGE_SIZE;
+
+		unmap_mapping_range(inode->i_mapping, start, len, 1);
+	}
+	owner = mds;
+	vfs_setlease(vma->vm_file, F_UNLCK, NULL, &owner);
+
+	put_map_direct(mds);
+}
+
+static bool map_direct_lm_break(struct file_lock *fl)
+{
+	struct map_direct_state *mds = fl->fl_owner;
+
+	/*
+	 * Given that we need to take sleeping locks to invalidate the
+	 * mapping we schedule that work with the original timeout set
+	 * by the file-locks core. Then we tell the core to hold off on
+	 * continuing with the lease break until the delayed work
+	 * completes the invalidation and the lease unlock.
+	 *
+	 * Note that this assumes that i_mapdcount is protecting against
+	 * block-map modifying write-faults since we are unable to use
+	 * leases in that path due to locking constraints.
+	 */
+	if (!test_and_set_bit(MAPDIRECT_BREAK, &mds->mds_state)) {
+		schedule_delayed_work(&mds->mds_work, lease_break_time * HZ);
+		kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
+	}
+
+	/* Tell the core lease code to wait for delayed work completion */
+	fl->fl_break_time = 0;
+
+	return false;
+}
+
+static int map_direct_lm_change(struct file_lock *fl, int arg,
+		struct list_head *dispose)
+{
+	struct map_direct_state *mds = fl->fl_owner;
+
+	WARN_ON(!(arg & F_UNLCK));
+
+	i_mapdcount_dec(mds->mds_inode);
+	return lease_modify(fl, arg, dispose);
+}
+
+static void map_direct_lm_setup(struct file_lock *fl, void **priv)
+{
+	struct file *file = fl->fl_file;
+	struct map_direct_state *mds = *priv;
+	struct fasync_struct *fa = mds->mds_fa;
+
+	/*
+	 * Comment copied from lease_setup():
+	 * fasync_insert_entry() returns the old entry if any. If there was no
+	 * old entry, then it used "priv" and inserted it into the fasync list.
+	 * Clear the pointer to indicate that it shouldn't be freed.
+	 */
+	if (!fasync_insert_entry(fa->fa_fd, file, &fl->fl_fasync, fa))
+		*priv = NULL;
+
+	__f_setown(file, task_pid(current), PIDTYPE_PID, 0);
+}
+
+static const struct lock_manager_operations map_direct_lm_ops = {
+	.lm_break = map_direct_lm_break,
+	.lm_change = map_direct_lm_change,
+	.lm_setup = map_direct_lm_setup,
+};
+
+struct map_direct_state *map_direct_register(int fd, struct vm_area_struct *vma)
+{
+	struct map_direct_state *mds = kzalloc(sizeof(*mds), GFP_KERNEL);
+	struct file *file = vma->vm_file;
+	struct inode *inode = file_inode(file);
+	struct fasync_struct *fa;
+	struct file_lock *fl;
+	void *owner = mds;
+	int rc = -ENOMEM;
+
+	if (!mds)
+		return ERR_PTR(-ENOMEM);
+
+	mds->mds_vma = vma;
+	atomic_set(&mds->mds_ref, 1);
+	atomic_set(&mds->mds_vmaref, 1);
+	set_bit(MAPDIRECT_VALID, &mds->mds_state);
+	mds->mds_inode = inode;
+	ihold(inode);
+	INIT_DELAYED_WORK(&mds->mds_work, map_direct_invalidate);
+
+	fa = fasync_alloc();
+	if (!fa)
+		goto err_fasync_alloc;
+	mds->mds_fa = fa;
+	fa->fa_fd = fd;
+
+	fl = locks_alloc_lock();
+	if (!fl)
+		goto err_lock_alloc;
+
+	locks_init_lock(fl);
+	fl->fl_lmops = &map_direct_lm_ops;
+	fl->fl_flags = FL_LAYOUT;
+	fl->fl_type = F_RDLCK;
+	fl->fl_end = OFFSET_MAX;
+	fl->fl_owner = mds;
+	atomic_inc(&mds->mds_ref);
+	fl->fl_pid = current->tgid;
+	fl->fl_file = file;
+
+	rc = vfs_setlease(file, fl->fl_type, &fl, &owner);
+	if (rc)
+		goto err_setlease;
+	if (fl) {
+		WARN_ON(1);
+		owner = mds;
+		vfs_setlease(file, F_UNLCK, NULL, &owner);
+		owner = NULL;
+		rc = -ENXIO;
+		goto err_setlease;
+	}
+
+	i_mapdcount_inc(inode);
+	return mds;
+
+err_setlease:
+	locks_free_lock(fl);
+err_lock_alloc:
+	/* if owner is NULL then the lease machinery is reponsible @fa */
+	if (owner)
+		fasync_free(fa);
+err_fasync_alloc:
+	iput(inode);
+	kfree(mds);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_GPL(map_direct_register);
diff --git a/include/linux/mapdirect.h b/include/linux/mapdirect.h
new file mode 100644
index 000000000000..724e27d8615e
--- /dev/null
+++ b/include/linux/mapdirect.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#ifndef __MAPDIRECT_H__
+#define __MAPDIRECT_H__
+#include <linux/err.h>
+
+struct inode;
+struct work_struct;
+struct vm_area_struct;
+struct map_direct_state;
+
+#if IS_ENABLED(CONFIG_FS_DAX)
+struct map_direct_state *map_direct_register(int fd, struct vm_area_struct *vma);
+int put_map_direct_vma(struct map_direct_state *mds);
+void get_map_direct_vma(struct map_direct_state *mds);
+bool is_map_direct_valid(struct map_direct_state *mds);
+#else
+static inline struct map_direct_state *map_direct_register(int fd,
+		struct vm_area_struct *vma)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+int put_map_direct_vma(struct map_direct_state *mds)
+{
+	return 0;
+}
+static inline void get_map_direct_vma(struct map_direct_state *mds)
+{
+}
+bool is_map_direct_valid(struct map_direct_state *mds)
+{
+	return false;
+}
+#endif
+#endif /* __MAPDIRECT_H__ */

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