mm: swapoff: shmem_unuse() stop eviction without igrab()

[thirdparty/linux.git] / mm / shmem.c

diff --git a/mm/shmem.c b/mm/shmem.c
index 859e8628071f19c51a6eb65d2197809f43044ab1..2275a0ff7c3051d9674ee59b153451c6078741c3 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1081,9 +1081,14 @@ static void shmem_evict_inode(struct inode *inode)
                        }
                        spin_unlock(&sbinfo->shrinklist_lock);
                }
-               if (!list_empty(&info->swaplist)) {
+               while (!list_empty(&info->swaplist)) {
+                       /* Wait while shmem_unuse() is scanning this inode... */
+                       wait_var_event(&info->stop_eviction,
+                                      !atomic_read(&info->stop_eviction));
                        mutex_lock(&shmem_swaplist_mutex);
-                       list_del_init(&info->swaplist);
+                       /* ...but beware of the race if we peeked too early */
+                       if (!atomic_read(&info->stop_eviction))
+                               list_del_init(&info->swaplist);
                        mutex_unlock(&shmem_swaplist_mutex);
                }
        }
@@ -1227,36 +1232,27 @@ int shmem_unuse(unsigned int type, bool frontswap,
                unsigned long *fs_pages_to_unuse)
 {
        struct shmem_inode_info *info, *next;
-       struct inode *inode;
-       struct inode *prev_inode = NULL;
        int error = 0;
 
        if (list_empty(&shmem_swaplist))
                return 0;
 
        mutex_lock(&shmem_swaplist_mutex);
-
-       /*
-        * The extra refcount on the inode is necessary to safely dereference
-        * p->next after re-acquiring the lock. New shmem inodes with swap
-        * get added to the end of the list and we will scan them all.
-        */
        list_for_each_entry_safe(info, next, &shmem_swaplist, swaplist) {
                if (!info->swapped) {
                        list_del_init(&info->swaplist);
                        continue;
                }
-
-               inode = igrab(&info->vfs_inode);
-               if (!inode)
-                       continue;
-
+               /*
+                * Drop the swaplist mutex while searching the inode for swap;
+                * but before doing so, make sure shmem_evict_inode() will not
+                * remove placeholder inode from swaplist, nor let it be freed
+                * (igrab() would protect from unlink, but not from unmount).
+                */
+               atomic_inc(&info->stop_eviction);
                mutex_unlock(&shmem_swaplist_mutex);
-               if (prev_inode)
-                       iput(prev_inode);
-               prev_inode = inode;
 
-               error = shmem_unuse_inode(inode, type, frontswap,
+               error = shmem_unuse_inode(&info->vfs_inode, type, frontswap,
                                          fs_pages_to_unuse);
                cond_resched();
 
@@ -1264,14 +1260,13 @@ int shmem_unuse(unsigned int type, bool frontswap,
                next = list_next_entry(info, swaplist);
                if (!info->swapped)
                        list_del_init(&info->swaplist);
+               if (atomic_dec_and_test(&info->stop_eviction))
+                       wake_up_var(&info->stop_eviction);
                if (error)
                        break;
        }
        mutex_unlock(&shmem_swaplist_mutex);
 
-       if (prev_inode)
-               iput(prev_inode);
-
        return error;
 }
 
@@ -2238,6 +2233,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
                info = SHMEM_I(inode);
                memset(info, 0, (char *)inode - (char *)info);
                spin_lock_init(&info->lock);
+               atomic_set(&info->stop_eviction, 0);
                info->seals = F_SEAL_SEAL;
                info->flags = flags & VM_NORESERVE;
                INIT_LIST_HEAD(&info->shrinklist);