Commit 3a7d2fd1 authored by Kees Cook's avatar Kees Cook
Browse files

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: default avatarMarta Lofstedt <marta.lofstedt@intel.com>
Reported-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 041939c1

fs/pstore/inode.c

+27 −10
Original line number Diff line number Diff line
@@ -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;

fs/pstore/internal.h

+4 −1
Original line number Diff line number Diff line
@@ -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

fs/pstore/platform.c

+5 −5
Original line number Diff line number Diff line
@@ -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);

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