Add logic to free up a busy memory range. Freed memory range will be
returned to free pool. Add a worker which can be started to select
and free some busy memory ranges.

Process can also steal one of its busy dax ranges if free range is not
available. I will refer it to as direct reclaim.

If free range is not available and nothing can't be stolen from same
inode, caller waits on a waitq for free range to become available.

For reclaiming a range, as of now we need to hold following locks in
specified order.

        down_write(&fi->i_mmap_sem);
        down_write(&fi->i_dmap_sem);

We look for a free range in following order.

A. Try to get a free range.
B. If not, try direct reclaim.
C. If not, wait for a memory range to become free

Signed-off-by: Vivek Goyal <[email protected]>
Signed-off-by: Liu Bo <[email protected]>
---
 fs/fuse/file.c   | 450 ++++++++++++++++++++++++++++++++++++++++++++++-
 fs/fuse/fuse_i.h |  25 +++
 fs/fuse/inode.c  |   5 +
 3 files changed, 473 insertions(+), 7 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 8b264fcb9b3c..61ae2ddeef55 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -8,6 +8,7 @@
 
 #include "fuse_i.h"
 
+#include <linux/delay.h>
 #include <linux/pagemap.h>
 #include <linux/slab.h>
 #include <linux/kernel.h>
@@ -37,6 +38,8 @@ static struct page **fuse_pages_alloc(unsigned int npages, 
gfp_t flags,
        return pages;
 }
 
+static struct fuse_dax_mapping *alloc_dax_mapping_reclaim(struct fuse_conn *fc,
+                               struct inode *inode, bool fault);
 static int fuse_send_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
                          int opcode, struct fuse_open_out *outargp)
 {
@@ -193,6 +196,28 @@ static void fuse_link_write_file(struct file *file)
        spin_unlock(&fi->lock);
 }
 
+static void
+__kick_dmap_free_worker(struct fuse_conn *fc, unsigned long delay_ms)
+{
+       unsigned long free_threshold;
+
+       /* If number of free ranges are below threshold, start reclaim */
+       free_threshold = max((fc->nr_ranges * FUSE_DAX_RECLAIM_THRESHOLD)/100,
+                               (unsigned long)1);
+       if (fc->nr_free_ranges < free_threshold) {
+               pr_debug("fuse: Kicking dax memory reclaim worker. 
nr_free_ranges=0x%ld nr_total_ranges=%ld\n", fc->nr_free_ranges, fc->nr_ranges);
+               queue_delayed_work(system_long_wq, &fc->dax_free_work,
+                                  msecs_to_jiffies(delay_ms));
+       }
+}
+
+static void kick_dmap_free_worker(struct fuse_conn *fc, unsigned long delay_ms)
+{
+       spin_lock(&fc->lock);
+       __kick_dmap_free_worker(fc, delay_ms);
+       spin_unlock(&fc->lock);
+}
+
 static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn *fc)
 {
        struct fuse_dax_mapping *dmap = NULL;
@@ -201,7 +226,7 @@ static struct fuse_dax_mapping *alloc_dax_mapping(struct 
fuse_conn *fc)
 
        if (fc->nr_free_ranges <= 0) {
                spin_unlock(&fc->lock);
-               return NULL;
+               goto out_kick;
        }
 
        WARN_ON(list_empty(&fc->free_ranges));
@@ -212,6 +237,9 @@ static struct fuse_dax_mapping *alloc_dax_mapping(struct 
fuse_conn *fc)
        list_del_init(&dmap->list);
        fc->nr_free_ranges--;
        spin_unlock(&fc->lock);
+
+out_kick:
+       kick_dmap_free_worker(fc, 0);
        return dmap;
 }
 
@@ -238,6 +266,7 @@ static void __dmap_add_to_free_pool(struct fuse_conn *fc,
 {
        list_add_tail(&dmap->list, &fc->free_ranges);
        fc->nr_free_ranges++;
+       wake_up(&fc->dax_range_waitq);
 }
 
 static void dmap_add_to_free_pool(struct fuse_conn *fc,
@@ -289,6 +318,12 @@ static int fuse_setup_one_mapping(struct inode *inode, 
loff_t offset,
 
        dmap->writable = writable;
        if (!upgrade) {
+               /*
+                * We don't take a refernce on inode. inode is valid right now
+                * and when inode is going away, cleanup logic should first
+                * cleanup dmap entries.
+                */
+               dmap->inode = inode;
                dmap->start = offset;
                dmap->end = offset + FUSE_DAX_MEM_RANGE_SZ - 1;
                /* Protected by fi->i_dmap_sem */
@@ -368,6 +403,7 @@ static void dmap_reinit_add_to_free_pool(struct fuse_conn 
*fc,
                 "window_offset=0x%llx length=0x%llx\n", dmap->start,
                 dmap->end, dmap->window_offset, dmap->length);
        __dmap_remove_busy_list(fc, dmap);
+       dmap->inode = NULL;
        dmap->start = dmap->end = 0;
        __dmap_add_to_free_pool(fc, dmap);
 }
@@ -386,7 +422,8 @@ static void inode_reclaim_dmap_range(struct fuse_conn *fc, 
struct inode *inode,
        int err, num = 0;
        LIST_HEAD(to_remove);
 
-       pr_debug("fuse: %s: start=0x%llx, end=0x%llx\n", __func__, start, end);
+       pr_debug("fuse: %s: inode=0x%px start=0x%llx, end=0x%llx\n", __func__,
+                inode, start, end);
 
        /*
         * Interval tree search matches intersecting entries. Adjust the range
@@ -400,6 +437,8 @@ static void inode_reclaim_dmap_range(struct fuse_conn *fc, 
struct inode *inode,
                                                         end);
                if (!dmap)
                        break;
+               /* inode is going away. There should not be any users of dmap */
+               WARN_ON(refcount_read(&dmap->refcnt) > 1);
                fuse_dax_interval_tree_remove(dmap, &fi->dmap_tree);
                num++;
                list_add(&dmap->list, &to_remove);
@@ -434,6 +473,21 @@ static void inode_reclaim_dmap_range(struct fuse_conn *fc, 
struct inode *inode,
        spin_unlock(&fc->lock);
 }
 
+static int dmap_removemapping_one(struct inode *inode,
+                                 struct fuse_dax_mapping *dmap)
+{
+       struct fuse_removemapping_one forget_one;
+       struct fuse_removemapping_in inarg;
+
+       memset(&inarg, 0, sizeof(inarg));
+       inarg.count = 1;
+       memset(&forget_one, 0, sizeof(forget_one));
+       forget_one.moffset = dmap->window_offset;
+       forget_one.len = dmap->length;
+
+       return fuse_send_removemapping(inode, &inarg, &forget_one);
+}
+
 /*
  * It is called from evict_inode() and by that time inode is going away. So
  * this function does not take any locks like fi->i_dmap_sem for traversing
@@ -1903,6 +1957,17 @@ static void fuse_fill_iomap(struct inode *inode, loff_t 
pos, loff_t length,
                if (flags & IOMAP_FAULT)
                        iomap->length = ALIGN(len, PAGE_SIZE);
                iomap->type = IOMAP_MAPPED;
+               /*
+                * increace refcnt so that reclaim code knows this dmap is in
+                * use. This assumes i_dmap_sem mutex is held either
+                * shared/exclusive.
+                */
+               refcount_inc(&dmap->refcnt);
+
+               /* iomap->private should be NULL */
+               WARN_ON_ONCE(iomap->private);
+               iomap->private = dmap;
+
                pr_debug("%s: returns iomap: addr 0x%llx offset 0x%llx"
                                " length 0x%llx\n", __func__, iomap->addr,
                                iomap->offset, iomap->length);
@@ -1925,8 +1990,12 @@ static int iomap_begin_setup_new_mapping(struct inode 
*inode, loff_t pos,
        int ret;
        bool writable = flags & IOMAP_WRITE;
 
-       alloc_dmap = alloc_dax_mapping(fc);
-       if (!alloc_dmap)
+       alloc_dmap = alloc_dax_mapping_reclaim(fc, inode, flags & IOMAP_FAULT);
+       if (IS_ERR(alloc_dmap))
+               return PTR_ERR(alloc_dmap);
+
+       /* If we are here, we should have memory allocated */
+       if (WARN_ON(!alloc_dmap))
                return -EBUSY;
 
        /*
@@ -1979,14 +2048,25 @@ static int iomap_begin_upgrade_mapping(struct inode 
*inode, loff_t pos,
        dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, pos, pos);
 
        /* We are holding either inode lock or i_mmap_sem, and that should
-        * ensure that dmap can't reclaimed or truncated and it should still
-        * be there in tree despite the fact we dropped and re-acquired the
-        * lock.
+        * ensure that dmap can't be truncated. We are holding a reference
+        * on dmap and that should make sure it can't be reclaimed. So dmap
+        * should still be there in tree despite the fact we dropped and
+        * re-acquired the i_dmap_sem lock.
         */
        ret = -EIO;
        if (WARN_ON(!dmap))
                goto out_err;
 
+       /* We took an extra reference on dmap to make sure its not reclaimd.
+        * Now we hold i_dmap_sem lock and that reference is not needed
+        * anymore. Drop it.
+        */
+       if (refcount_dec_and_test(&dmap->refcnt)) {
+               /* refcount should not hit 0. This object only goes
+                * away when fuse connection goes away */
+               WARN_ON_ONCE(1);
+       }
+
        /* Maybe another thread already upgraded mapping while we were not
         * holding lock.
         */
@@ -2056,7 +2136,11 @@ static int fuse_iomap_begin(struct inode *inode, loff_t 
pos, loff_t length,
                         * two threads to be trying to this simultaneously
                         * for same dmap. So drop shared lock and acquire
                         * exclusive lock.
+                        *
+                        * Before dropping i_dmap_sem lock, take reference
+                        * on dmap so that its not freed by range reclaim.
                         */
+                       refcount_inc(&dmap->refcnt);
                        up_read(&fi->i_dmap_sem);
                        pr_debug("%s: Upgrading mapping at offset 0x%llx"
                                 " length 0x%llx\n", __func__, pos, length);
@@ -2092,6 +2176,16 @@ static int fuse_iomap_end(struct inode *inode, loff_t 
pos, loff_t length,
                          ssize_t written, unsigned flags,
                          struct iomap *iomap)
 {
+       struct fuse_dax_mapping *dmap = iomap->private;
+
+       if (dmap) {
+               if (refcount_dec_and_test(&dmap->refcnt)) {
+                       /* refcount should not hit 0. This object only goes
+                        * away when fuse connection goes away */
+                       WARN_ON_ONCE(1);
+               }
+       }
+
        /* DAX writes beyond end-of-file aren't handled using iomap, so the
         * file size is unchanged and there is nothing to do here.
         */
@@ -4103,3 +4197,345 @@ void fuse_init_file_inode(struct inode *inode)
                inode->i_data.a_ops = &fuse_dax_file_aops;
        }
 }
+
+static int dmap_writeback_invalidate(struct inode *inode,
+                                    struct fuse_dax_mapping *dmap)
+{
+       int ret;
+
+       ret = filemap_fdatawrite_range(inode->i_mapping, dmap->start,
+                                      dmap->end);
+       if (ret) {
+               printk("filemap_fdatawrite_range() failed. err=%d start=0x%llx,"
+                       " end=0x%llx\n", ret, dmap->start, dmap->end);
+               return ret;
+       }
+
+       ret = invalidate_inode_pages2_range(inode->i_mapping,
+                                           dmap->start >> PAGE_SHIFT,
+                                           dmap->end >> PAGE_SHIFT);
+       if (ret)
+               printk("invalidate_inode_pages2_range() failed err=%d\n", ret);
+
+       return ret;
+}
+
+static int reclaim_one_dmap_locked(struct fuse_conn *fc, struct inode *inode,
+                                  struct fuse_dax_mapping *dmap)
+{
+       int ret;
+       struct fuse_inode *fi = get_fuse_inode(inode);
+
+       /*
+        * igrab() was done to make sure inode won't go under us, and this
+        * further avoids the race with evict().
+        */
+       ret = dmap_writeback_invalidate(inode, dmap);
+       if (ret)
+               return ret;
+
+       /* Remove dax mapping from inode interval tree now */
+       fuse_dax_interval_tree_remove(dmap, &fi->dmap_tree);
+       fi->nr_dmaps--;
+
+       /* It is possible that umount/shutodwn has killed the fuse connection
+        * and worker thread is trying to reclaim memory in parallel. So check
+        * if connection is still up or not otherwise don't send removemapping
+        * message.
+        */
+       if (fc->connected) {
+               ret = dmap_removemapping_one(inode, dmap);
+               if (ret) {
+                       pr_warn("Failed to remove mapping. offset=0x%llx"
+                               " len=0x%llx ret=%d\n", dmap->window_offset,
+                               dmap->length, ret);
+               }
+       }
+       return 0;
+}
+
+static void fuse_wait_dax_page(struct inode *inode)
+{
+       struct fuse_inode *fi = get_fuse_inode(inode);
+
+        up_write(&fi->i_mmap_sem);
+        schedule();
+        down_write(&fi->i_mmap_sem);
+}
+
+/* Should be called with fi->i_mmap_sem lock held exclusively */
+static int __fuse_break_dax_layouts(struct inode *inode, bool *retry,
+                                   loff_t start, loff_t end)
+{
+       struct page *page;
+
+       page = dax_layout_busy_page_range(inode->i_mapping, start, end);
+       if (!page)
+               return 0;
+
+       *retry = true;
+       return ___wait_var_event(&page->_refcount,
+                       atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
+                       0, 0, fuse_wait_dax_page(inode));
+}
+
+/* dmap_end == 0 leads to unmapping of whole file */
+static int fuse_break_dax_layouts(struct inode *inode, u64 dmap_start,
+                                 u64 dmap_end)
+{
+       bool    retry;
+       int     ret;
+
+       do {
+               retry = false;
+               ret = __fuse_break_dax_layouts(inode, &retry, dmap_start,
+                                              dmap_end);
+        } while (ret == 0 && retry);
+
+        return ret;
+}
+
+/* Find first mapping in the tree and free it. */
+static struct fuse_dax_mapping *
+inode_reclaim_one_dmap_locked(struct fuse_conn *fc, struct inode *inode)
+{
+       struct fuse_inode *fi = get_fuse_inode(inode);
+       struct fuse_dax_mapping *dmap;
+       int ret;
+
+       for (dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, 0, -1);
+            dmap;
+            dmap = fuse_dax_interval_tree_iter_next(dmap, 0, -1)) {
+               /* still in use. */
+               if (refcount_read(&dmap->refcnt) > 1)
+                       continue;
+
+               ret = reclaim_one_dmap_locked(fc, inode, dmap);
+               if (ret < 0)
+                       return ERR_PTR(ret);
+
+               /* Clean up dmap. Do not add back to free list */
+               dmap_remove_busy_list(fc, dmap);
+               dmap->inode = NULL;
+               dmap->start = dmap->end = 0;
+
+               pr_debug("fuse: %s: reclaimed memory range. inode=%px,"
+                        " window_offset=0x%llx, length=0x%llx\n", __func__,
+                        inode, dmap->window_offset, dmap->length);
+               return dmap;
+       }
+
+       return NULL;
+}
+
+/*
+ * Find first mapping in the tree and free it and return it. Do not add
+ * it back to free pool. If fault == true, this function should be called
+ * with fi->i_mmap_sem held.
+ */
+static struct fuse_dax_mapping *inode_reclaim_one_dmap(struct fuse_conn *fc,
+                                                        struct inode *inode,
+                                                        bool fault)
+{
+       struct fuse_inode *fi = get_fuse_inode(inode);
+       struct fuse_dax_mapping *dmap;
+       int ret;
+
+       if (!fault)
+               down_write(&fi->i_mmap_sem);
+
+       /*
+        * Make sure there are no references to inode pages using
+        * get_user_pages()
+        */
+       ret = fuse_break_dax_layouts(inode, 0, 0);
+       if (ret) {
+               printk("virtio_fs: fuse_break_dax_layouts() failed. err=%d\n",
+                      ret);
+               dmap = ERR_PTR(ret);
+               goto out_mmap_sem;
+       }
+       down_write(&fi->i_dmap_sem);
+       dmap = inode_reclaim_one_dmap_locked(fc, inode);
+       up_write(&fi->i_dmap_sem);
+out_mmap_sem:
+       if (!fault)
+               up_write(&fi->i_mmap_sem);
+       return dmap;
+}
+
+/* If fault == true, it should be called with fi->i_mmap_sem locked */
+static struct fuse_dax_mapping *alloc_dax_mapping_reclaim(struct fuse_conn *fc,
+                                       struct inode *inode, bool fault)
+{
+       struct fuse_dax_mapping *dmap;
+       struct fuse_inode *fi = get_fuse_inode(inode);
+
+       while(1) {
+               dmap = alloc_dax_mapping(fc);
+               if (dmap)
+                       return dmap;
+
+               if (fi->nr_dmaps) {
+                       dmap = inode_reclaim_one_dmap(fc, inode, fault);
+                       if (dmap)
+                               return dmap;
+                       /* If we could not reclaim a mapping because it
+                        * had a reference, that should be a temporary
+                        * situation. Try again.
+                        */
+                       msleep(1);
+                       continue;
+               }
+               /*
+                * There are no mappings which can be reclaimed.
+                * Wait for one.
+                */
+               if (!(fc->nr_free_ranges > 0)) {
+                       if (wait_event_killable_exclusive(fc->dax_range_waitq,
+                                       (fc->nr_free_ranges > 0)))
+                               return ERR_PTR(-EINTR);
+               }
+       }
+}
+
+static int lookup_and_reclaim_dmap_locked(struct fuse_conn *fc,
+                                         struct inode *inode, u64 dmap_start)
+{
+       int ret;
+       struct fuse_inode *fi = get_fuse_inode(inode);
+       struct fuse_dax_mapping *dmap;
+
+       /* Find fuse dax mapping at file offset inode. */
+       dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, dmap_start,
+                                                dmap_start);
+
+       /* Range already got cleaned up by somebody else */
+       if (!dmap)
+               return 0;
+
+       /* still in use. */
+       if (refcount_read(&dmap->refcnt) > 1)
+               return 0;
+
+       ret = reclaim_one_dmap_locked(fc, inode, dmap);
+       if (ret < 0)
+               return ret;
+
+       /* Cleanup dmap entry and add back to free list */
+       spin_lock(&fc->lock);
+       dmap_reinit_add_to_free_pool(fc, dmap);
+       spin_unlock(&fc->lock);
+       return ret;
+}
+
+/*
+ * Free a range of memory.
+ * Locking.
+ * 1. Take fuse_inode->i_mmap_sem to block dax faults.
+ * 2. Take fuse_inode->i_dmap_sem to protect interval tree and also to make
+ *    sure read/write can not reuse a dmap which we might be freeing.
+ */
+static int lookup_and_reclaim_dmap(struct fuse_conn *fc, struct inode *inode,
+                                  u64 dmap_start, u64 dmap_end)
+{
+       int ret;
+       struct fuse_inode *fi = get_fuse_inode(inode);
+
+       down_write(&fi->i_mmap_sem);
+       ret = fuse_break_dax_layouts(inode, dmap_start, dmap_end);
+       if (ret) {
+               printk("virtio_fs: fuse_break_dax_layouts() failed. err=%d\n",
+                      ret);
+               goto out_mmap_sem;
+       }
+
+       down_write(&fi->i_dmap_sem);
+       ret = lookup_and_reclaim_dmap_locked(fc, inode, dmap_start);
+       up_write(&fi->i_dmap_sem);
+out_mmap_sem:
+       up_write(&fi->i_mmap_sem);
+       return ret;
+}
+
+static int try_to_free_dmap_chunks(struct fuse_conn *fc,
+                                  unsigned long nr_to_free)
+{
+       struct fuse_dax_mapping *dmap, *pos, *temp;
+       int ret, nr_freed = 0;
+       u64 dmap_start = 0, window_offset = 0, dmap_end = 0;
+       struct inode *inode = NULL;
+
+       /* Pick first busy range and free it for now*/
+       while(1) {
+               if (nr_freed >= nr_to_free)
+                       break;
+
+               dmap = NULL;
+               spin_lock(&fc->lock);
+
+               if (!fc->nr_busy_ranges) {
+                       spin_unlock(&fc->lock);
+                       return 0;
+               }
+
+               list_for_each_entry_safe(pos, temp, &fc->busy_ranges,
+                                               busy_list) {
+                       /* skip this range if it's in use. */
+                       if (refcount_read(&pos->refcnt) > 1)
+                               continue;
+
+                       inode = igrab(pos->inode);
+                       /*
+                        * This inode is going away. That will free
+                        * up all the ranges anyway, continue to
+                        * next range.
+                        */
+                       if (!inode)
+                               continue;
+                       /*
+                        * Take this element off list and add it tail. If
+                        * this element can't be freed, it will help with
+                        * selecting new element in next iteration of loop.
+                        */
+                       dmap = pos;
+                       list_move_tail(&dmap->busy_list, &fc->busy_ranges);
+                       dmap_start = dmap->start;
+                       dmap_end = dmap->end;
+                       window_offset = dmap->window_offset;
+                       break;
+               }
+               spin_unlock(&fc->lock);
+               if (!dmap)
+                       return 0;
+
+               ret = lookup_and_reclaim_dmap(fc, inode, dmap_start, dmap_end);
+               iput(inode);
+               if (ret) {
+                       printk("%s(window_offset=0x%llx) failed. err=%d\n",
+                               __func__, window_offset, ret);
+                       return ret;
+               }
+               nr_freed++;
+       }
+       return 0;
+}
+
+void fuse_dax_free_mem_worker(struct work_struct *work)
+{
+       int ret;
+       struct fuse_conn *fc = container_of(work, struct fuse_conn,
+                                               dax_free_work.work);
+       pr_debug("fuse: Worker to free memory called. nr_free_ranges=%lu"
+                " nr_busy_ranges=%lu\n", fc->nr_free_ranges,
+                fc->nr_busy_ranges);
+
+       ret = try_to_free_dmap_chunks(fc, FUSE_DAX_RECLAIM_CHUNK);
+       if (ret) {
+               pr_debug("fuse: try_to_free_dmap_chunks() failed with err=%d\n",
+                        ret);
+       }
+
+       /* If number of free ranges are still below threhold, requeue */
+       kick_dmap_free_worker(fc, 1);
+}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index de213a7e1b0e..41c2fbff0d37 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -54,6 +54,16 @@
 #define FUSE_DAX_MEM_RANGE_SZ  (2*1024*1024)
 #define FUSE_DAX_MEM_RANGE_PAGES       (FUSE_DAX_MEM_RANGE_SZ/PAGE_SIZE)
 
+/* Number of ranges reclaimer will try to free in one invocation */
+#define FUSE_DAX_RECLAIM_CHUNK         (10)
+
+/*
+ * Dax memory reclaim threshold in percetage of total ranges. When free
+ * number of free ranges drops below this threshold, reclaim can trigger
+ * Default is 20%
+ * */
+#define FUSE_DAX_RECLAIM_THRESHOLD     (20)
+
 /** List of active connections */
 extern struct list_head fuse_conn_list;
 
@@ -75,6 +85,9 @@ struct fuse_forget_link {
 
 /** Translation information for file offsets to DAX window offsets */
 struct fuse_dax_mapping {
+       /* Pointer to inode where this memory range is mapped */
+       struct inode *inode;
+
        /* Will connect in fc->free_ranges to keep track of free memory */
        struct list_head list;
 
@@ -97,6 +110,9 @@ struct fuse_dax_mapping {
 
        /* Is this mapping read-only or read-write */
        bool writable;
+
+       /* reference count when the mapping is used by dax iomap. */
+       refcount_t refcnt;
 };
 
 /** FUSE inode */
@@ -822,11 +838,19 @@ struct fuse_conn {
        unsigned long nr_busy_ranges;
        struct list_head busy_ranges;
 
+       /* Worker to free up memory ranges */
+       struct delayed_work dax_free_work;
+
+       /* Wait queue for a dax range to become free */
+       wait_queue_head_t dax_range_waitq;
+
        /*
         * DAX Window Free Ranges
         */
        long nr_free_ranges;
        struct list_head free_ranges;
+
+       unsigned long nr_ranges;
 };
 
 static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
@@ -1164,6 +1188,7 @@ unsigned int fuse_len_args(unsigned int numargs, struct 
fuse_arg *args);
  */
 u64 fuse_get_unique(struct fuse_iqueue *fiq);
 void fuse_free_conn(struct fuse_conn *fc);
+void fuse_dax_free_mem_worker(struct work_struct *work);
 void fuse_cleanup_inode_mappings(struct inode *inode);
 
 #endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index d4770e7fb7eb..3560b62077a7 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -663,11 +663,13 @@ static int fuse_dax_mem_range_init(struct fuse_conn *fc,
                range->window_offset = i * FUSE_DAX_MEM_RANGE_SZ;
                range->length = FUSE_DAX_MEM_RANGE_SZ;
                INIT_LIST_HEAD(&range->busy_list);
+               refcount_set(&range->refcnt, 1);
                list_add_tail(&range->list, &mem_ranges);
        }
 
        list_replace_init(&mem_ranges, &fc->free_ranges);
        fc->nr_free_ranges = nr_ranges;
+       fc->nr_ranges = nr_ranges;
        return 0;
 out_err:
        /* Free All allocated elements */
@@ -692,6 +694,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct 
user_namespace *user_ns,
        refcount_set(&fc->count, 1);
        atomic_set(&fc->dev_count, 1);
        init_waitqueue_head(&fc->blocked_waitq);
+       init_waitqueue_head(&fc->dax_range_waitq);
        fuse_iqueue_init(&fc->iq, fiq_ops, fiq_priv);
        INIT_LIST_HEAD(&fc->bg_queue);
        INIT_LIST_HEAD(&fc->entry);
@@ -711,6 +714,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct 
user_namespace *user_ns,
        fc->max_pages = FUSE_DEFAULT_MAX_PAGES_PER_REQ;
        INIT_LIST_HEAD(&fc->free_ranges);
        INIT_LIST_HEAD(&fc->busy_ranges);
+       INIT_DELAYED_WORK(&fc->dax_free_work, fuse_dax_free_mem_worker);
 }
 EXPORT_SYMBOL_GPL(fuse_conn_init);
 
@@ -719,6 +723,7 @@ void fuse_conn_put(struct fuse_conn *fc)
        if (refcount_dec_and_test(&fc->count)) {
                struct fuse_iqueue *fiq = &fc->iq;
 
+               flush_delayed_work(&fc->dax_free_work);
                if (fc->dax_dev)
                        fuse_free_dax_mem_ranges(&fc->free_ranges);
                if (fiq->ops->release)
-- 
2.20.1

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