Merge branch 'for-chris-4.7' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux into for-linus-4.7

1 files changed, 61 insertions, 24 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index ff61a41ac90b..658c39b70fba 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -743,8 +743,11 @@ out:
 static struct {
         struct list_head idle_ws;
         spinlock_t ws_lock;
-        int num_ws;
-        atomic_t alloc_ws;
+        /* Number of free workspaces */
+        int free_ws;
+        /* Total number of allocated workspaces */
+        atomic_t total_ws;
+        /* Waiters for a free workspace */
         wait_queue_head_t ws_wait;
 } btrfs_comp_ws[BTRFS_COMPRESS_TYPES];
 
@@ -758,16 +761,34 @@ void __init btrfs_init_compress(void)
         int i;
 
         for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
+                struct list_head *workspace;
+
                 INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws);
                 spin_lock_init(&btrfs_comp_ws[i].ws_lock);
-                atomic_set(&btrfs_comp_ws[i].alloc_ws, 0);
+                atomic_set(&btrfs_comp_ws[i].total_ws, 0);
                 init_waitqueue_head(&btrfs_comp_ws[i].ws_wait);
+
+                /*
+                 * Preallocate one workspace for each compression type so
+                 * we can guarantee forward progress in the worst case
+                 */
+                workspace = btrfs_compress_op[i]->alloc_workspace();
+                if (IS_ERR(workspace)) {
+                        printk(KERN_WARNING
+        "BTRFS: cannot preallocate compression workspace, will try later");
+                } else {
+                        atomic_set(&btrfs_comp_ws[i].total_ws, 1);
+                        btrfs_comp_ws[i].free_ws = 1;
+                        list_add(workspace, &btrfs_comp_ws[i].idle_ws);
+                }
         }
 }
 
 /*
- * this finds an available workspace or allocates a new one
- * ERR_PTR is returned if things go bad.
+ * This finds an available workspace or allocates a new one.
+ * If it's not possible to allocate a new one, waits until there's one.
+ * Preallocation makes a forward progress guarantees and we do not return
+ * errors.
  */
 static struct list_head *find_workspace(int type)
 {
@@ -777,36 +798,58 @@ static struct list_head *find_workspace(int type)
 
         struct list_head *idle_ws       = &btrfs_comp_ws[idx].idle_ws;
         spinlock_t *ws_lock             = &btrfs_comp_ws[idx].ws_lock;
-        atomic_t *alloc_ws              = &btrfs_comp_ws[idx].alloc_ws;
+        atomic_t *total_ws              = &btrfs_comp_ws[idx].total_ws;
         wait_queue_head_t *ws_wait      = &btrfs_comp_ws[idx].ws_wait;
-        int *num_ws                     = &btrfs_comp_ws[idx].num_ws;
+        int *free_ws                    = &btrfs_comp_ws[idx].free_ws;
 again:
         spin_lock(ws_lock);
         if (!list_empty(idle_ws)) {
                 workspace = idle_ws->next;
                 list_del(workspace);
-                (*num_ws)--;
+                (*free_ws)--;
                 spin_unlock(ws_lock);
                 return workspace;
 
         }
-        if (atomic_read(alloc_ws) > cpus) {
+        if (atomic_read(total_ws) > cpus) {
                 DEFINE_WAIT(wait);
 
                 spin_unlock(ws_lock);
                 prepare_to_wait(ws_wait, &wait, TASK_UNINTERRUPTIBLE);
-                if (atomic_read(alloc_ws) > cpus && !*num_ws)
+                if (atomic_read(total_ws) > cpus && !*free_ws)
                         schedule();
                 finish_wait(ws_wait, &wait);
                 goto again;
         }
-        atomic_inc(alloc_ws);
+        atomic_inc(total_ws);
         spin_unlock(ws_lock);
 
         workspace = btrfs_compress_op[idx]->alloc_workspace();
         if (IS_ERR(workspace)) {
-                atomic_dec(alloc_ws);
+                atomic_dec(total_ws);
                 wake_up(ws_wait);
+
+                /*
+                 * Do not return the error but go back to waiting. There's a
+                 * workspace preallocated for each type and the compression
+                 * time is bounded so we get to a workspace eventually. This
+                 * makes our caller's life easier.
+                 *
+                 * To prevent silent and low-probability deadlocks (when the
+                 * initial preallocation fails), check if there are any
+                 * workspaces at all.
+                 */
+                if (atomic_read(total_ws) == 0) {
+                        static DEFINE_RATELIMIT_STATE(_rs,
+                                        /* once per minute */ 60 * HZ,
+                                        /* no burst */ 1);
+
+                        if (__ratelimit(&_rs)) {
+                                printk(KERN_WARNING
+                            "no compression workspaces, low memory, retrying");
+                        }
+                }
+                goto again;
         }
         return workspace;
 }
@@ -820,21 +863,21 @@ static void free_workspace(int type, struct list_head *workspace)
         int idx = type - 1;
         struct list_head *idle_ws       = &btrfs_comp_ws[idx].idle_ws;
         spinlock_t *ws_lock             = &btrfs_comp_ws[idx].ws_lock;
-        atomic_t *alloc_ws              = &btrfs_comp_ws[idx].alloc_ws;
+        atomic_t *total_ws              = &btrfs_comp_ws[idx].total_ws;
         wait_queue_head_t *ws_wait      = &btrfs_comp_ws[idx].ws_wait;
-        int *num_ws                     = &btrfs_comp_ws[idx].num_ws;
+        int *free_ws                    = &btrfs_comp_ws[idx].free_ws;
 
         spin_lock(ws_lock);
-        if (*num_ws < num_online_cpus()) {
+        if (*free_ws < num_online_cpus()) {
                 list_add(workspace, idle_ws);
-                (*num_ws)++;
+                (*free_ws)++;
                 spin_unlock(ws_lock);
                 goto wake;
         }
         spin_unlock(ws_lock);
 
         btrfs_compress_op[idx]->free_workspace(workspace);
-        atomic_dec(alloc_ws);
+        atomic_dec(total_ws);
 wake:
         /*
          * Make sure counter is updated before we wake up waiters.
@@ -857,7 +900,7 @@ static void free_workspaces(void)
                         workspace = btrfs_comp_ws[i].idle_ws.next;
                         list_del(workspace);
                         btrfs_compress_op[i]->free_workspace(workspace);
-                        atomic_dec(&btrfs_comp_ws[i].alloc_ws);
+                        atomic_dec(&btrfs_comp_ws[i].total_ws);
                 }
         }
 }
@@ -894,8 +937,6 @@ int btrfs_compress_pages(int type, struct address_space *mapping,
         int ret;
 
         workspace = find_workspace(type);
-        if (IS_ERR(workspace))
-                return PTR_ERR(workspace);
 
         ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
                                                       start, len, pages,
@@ -930,8 +971,6 @@ static int btrfs_decompress_biovec(int type, struct page **pages_in,
         int ret;
 
         workspace = find_workspace(type);
-        if (IS_ERR(workspace))
-                return PTR_ERR(workspace);
 
         ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
                                                          disk_start,
@@ -952,8 +991,6 @@ int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
         int ret;
 
         workspace = find_workspace(type);
-        if (IS_ERR(workspace))
-                return PTR_ERR(workspace);
 
         ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
                                                   dest_page, start_byte,