Re: [PATCH] pstore: Solve lockdep warning by moving inode locks

From: Namhyung Kim
Date: Thu Apr 27 2017 - 23:15:44 EST

Hi,

On Fri, Apr 28, 2017 at 8:20 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> 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@xxxxxxxxx>
> Reported-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Looks good to me!

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> ---
> fs/pstore/inode.c | 37 +++++++++++++++++++++++++++----------
> fs/pstore/internal.h | 5 ++++-
> fs/pstore/platform.c | 10 +++++-----
> 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 @@ int pstore_mkfile(struct pstore_record *record)
> 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);
> --
> 2.7.4
>
>
> --
> Kees Cook
> Pixel Security