pstore: Solve lockdep warning by moving inode locks

Lockdep complains about a possible deadlock between mount and unlink
(which is technically impossible), but fixing this improves possible
future multiple-backend support, and keeps locking in the right order.

The lockdep warning could be triggered by unlinking a file in the
pstore filesystem:

  -> #1 (&sb->s_type->i_mutex_key#14){++++++}:
         lock_acquire+0xc9/0x220
         down_write+0x3f/0x70
         pstore_mkfile+0x1f4/0x460
         pstore_get_records+0x17a/0x320
         pstore_fill_super+0xa4/0xc0
         mount_single+0x89/0xb0
         pstore_mount+0x13/0x20
         mount_fs+0xf/0x90
         vfs_kern_mount+0x66/0x170
         do_mount+0x190/0xd50
         SyS_mount+0x90/0xd0
         entry_SYSCALL_64_fastpath+0x1c/0xb1

  -> #0 (&psinfo->read_mutex){+.+.+.}:
         __lock_acquire+0x1ac0/0x1bb0
         lock_acquire+0xc9/0x220
         __mutex_lock+0x6e/0x990
         mutex_lock_nested+0x16/0x20
         pstore_unlink+0x3f/0xa0
         vfs_unlink+0xb5/0x190
         do_unlinkat+0x24c/0x2a0
         SyS_unlinkat+0x16/0x30
         entry_SYSCALL_64_fastpath+0x1c/0xb1

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&sb->s_type->i_mutex_key#14);
                                lock(&psinfo->read_mutex);
                                lock(&sb->s_type->i_mutex_key#14);
   lock(&psinfo->read_mutex);

Reported-by: Marta Lofstedt <marta.lofstedt@intel.com>
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>

3 files changed, 36 insertions, 16 deletions

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index 06504b69575b..792a4e5f9226 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -311,9 +311,8 @@ bool pstore_is_mounted(void)
  * Load it up with "size" bytes of data from "buf".
  * Set the mtime & ctime to the date that this record was originally stored.
  */
-int pstore_mkfile(struct pstore_record *record)
+int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 {
-        struct dentry           *root = pstore_sb->s_root;
         struct dentry           *dentry;
         struct inode            *inode;
         int                     rc = 0;
@@ -322,6 +321,8 @@ int pstore_mkfile(struct pstore_record *record)
         unsigned long           flags;
         size_t                  size = record->size + record->ecc_notice_size;
 
+        WARN_ON(!inode_is_locked(d_inode(root)));
+
         spin_lock_irqsave(&allpstore_lock, flags);
         list_for_each_entry(pos, &allpstore, list) {
                 if (pos->record->type == record->type &&
@@ -336,7 +337,7 @@ int pstore_mkfile(struct pstore_record *record)
                 return rc;
 
         rc = -ENOMEM;
-        inode = pstore_get_inode(pstore_sb);
+        inode = pstore_get_inode(root->d_sb);
         if (!inode)
                 goto fail;
         inode->i_mode = S_IFREG | 0444;
@@ -394,11 +395,9 @@ int pstore_mkfile(struct pstore_record *record)
                 break;
         }
 
-        inode_lock(d_inode(root));
-
         dentry = d_alloc_name(root, name);
         if (!dentry)
-                goto fail_lockedalloc;
+                goto fail_private;
 
         inode->i_size = private->total_size = size;
 
@@ -413,12 +412,9 @@ int pstore_mkfile(struct pstore_record *record)
         list_add(&private->list, &allpstore);
         spin_unlock_irqrestore(&allpstore_lock, flags);
 
-        inode_unlock(d_inode(root));
-
         return 0;
 
-fail_lockedalloc:
-        inode_unlock(d_inode(root));
+fail_private:
         free_pstore_private(private);
 fail_alloc:
         iput(inode);
@@ -427,6 +423,27 @@ fail:
         return rc;
 }
 
+/*
+ * Read all the records from the persistent store. Create
+ * files in our filesystem.  Don't warn about -EEXIST errors
+ * when we are re-scanning the backing store looking to add new
+ * error records.
+ */
+void pstore_get_records(int quiet)
+{
+        struct pstore_info *psi = psinfo;
+        struct dentry *root;
+
+        if (!psi || !pstore_sb)
+                return;
+
+        root = pstore_sb->s_root;
+
+        inode_lock(d_inode(root));
+        pstore_get_backend_records(psi, root, quiet);
+        inode_unlock(d_inode(root));
+}
+
 static int pstore_fill_super(struct super_block *sb, void *data, int silent)
 {
         struct inode *inode;
diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
index af1df5a36d86..c416e653dc4f 100644
--- a/fs/pstore/internal.h
+++ b/fs/pstore/internal.h
@@ -25,7 +25,10 @@ extern struct pstore_info *psinfo;
 
 extern void     pstore_set_kmsg_bytes(int);
 extern void     pstore_get_records(int);
-extern int      pstore_mkfile(struct pstore_record *record);
+extern void     pstore_get_backend_records(struct pstore_info *psi,
+                                           struct dentry *root, int quiet);
+extern int      pstore_mkfile(struct dentry *root,
+                              struct pstore_record *record);
 extern bool     pstore_is_mounted(void);
 
 #endif
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 43b3ca5e045f..d468eec9b8a6 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -810,17 +810,17 @@ static void decompress_record(struct pstore_record *record)
 }
 
 /*
- * Read all the records from the persistent store. Create
+ * Read all the records from one persistent store backend. Create
  * files in our filesystem.  Don't warn about -EEXIST errors
  * when we are re-scanning the backing store looking to add new
  * error records.
  */
-void pstore_get_records(int quiet)
+void pstore_get_backend_records(struct pstore_info *psi,
+                                struct dentry *root, int quiet)
 {
-        struct pstore_info *psi = psinfo;
         int failed = 0;
 
-        if (!psi)
+        if (!psi || !root)
                 return;
 
         mutex_lock(&psi->read_mutex);
@@ -850,7 +850,7 @@ void pstore_get_records(int quiet)
                         break;
 
                 decompress_record(record);
-                rc = pstore_mkfile(record);
+                rc = pstore_mkfile(root, record);
                 if (rc) {
                         /* pstore_mkfile() did not take record, so free it. */
                         kfree(record->buf);