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-rw-r--r--include/linux/shmem_fs.h1
-rw-r--r--mm/shmem.c40
-rw-r--r--mm/swapfile.c11
3 files changed, 24 insertions, 28 deletions
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index f3fb1edb3526..20d815a33145 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -21,6 +21,7 @@ struct shmem_inode_info {
struct list_head swaplist; /* chain of maybes on swap */
struct shared_policy policy; /* NUMA memory alloc policy */
struct simple_xattrs xattrs; /* list of xattrs */
+ atomic_t stop_eviction; /* hold when working on inode */
struct inode vfs_inode;
};
diff --git a/mm/shmem.c b/mm/shmem.c
index 859e8628071f..2275a0ff7c30 100644
--- 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);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 71383625a582..cf63b5f01adf 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2116,12 +2116,11 @@ retry:
* Under global memory pressure, swap entries can be reinserted back
* into process space after the mmlist loop above passes over them.
*
- * Limit the number of retries? No: when shmem_unuse()'s igrab() fails,
- * a shmem inode using swap is being evicted; and when mmget_not_zero()
- * above fails, that mm is likely to be freeing swap from exit_mmap().
- * Both proceed at their own independent pace: we could move them to
- * separate lists, and wait for those lists to be emptied; but it's
- * easier and more robust (though cpu-intensive) just to keep retrying.
+ * Limit the number of retries? No: when mmget_not_zero() above fails,
+ * that mm is likely to be freeing swap from exit_mmap(), which proceeds
+ * at its own independent pace; and even shmem_writepage() could have
+ * been preempted after get_swap_page(), temporarily hiding that swap.
+ * It's easy and robust (though cpu-intensive) just to keep retrying.
*/
if (si->inuse_pages) {
if (!signal_pending(current))