2017-06-29 7:01 GMT-07:00 Rabin Vincent <rabin.vincent@xxxxxxxx>:
> From: Rabin Vincent <rabinv@xxxxxxxx>
>
> When a CIFS filesystem is mounted with the forcemand option and the
> following command is run on it, lockdep warns about a circular locking
> dependency between CifsInodeInfo::lock_sem and the inode lock.
>
> while echo foo > hello; do :; done & while touch -c hello; do :; done
>
> cifs_writev() takes the locks in the wrong order, but note that we can't
> only flip the order around because it releases the inode lock before the
> call to generic_write_sync() while it holds the lock_sem across that
> call.
>
> But, AFAICS, there is no need to hold the CifsInodeInfo::lock_sem across
> the generic_write_sync() call either, so we can release both the locks
> before generic_write_sync(), and change the order.
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.12.0-rc7+ #9 Not tainted
> ------------------------------------------------------
> touch/487 is trying to acquire lock:
> (&cifsi->lock_sem){++++..}, at: cifsFileInfo_put+0x88f/0x16a0
>
> but task is already holding lock:
> (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&sb->s_type->i_mutex_key#11){+.+.+.}:
> __lock_acquire+0x1f74/0x38f0
> lock_acquire+0x1cc/0x600
> down_write+0x74/0x110
> cifs_strict_writev+0x3cb/0x8c0
> __vfs_write+0x4c1/0x930
> vfs_write+0x14c/0x2d0
> SyS_write+0xf7/0x240
> entry_SYSCALL_64_fastpath+0x1f/0xbe
>
> -> #0 (&cifsi->lock_sem){++++..}:
> check_prevs_add+0xfa0/0x1d10
> __lock_acquire+0x1f74/0x38f0
> lock_acquire+0x1cc/0x600
> down_write+0x74/0x110
> cifsFileInfo_put+0x88f/0x16a0
> cifs_setattr+0x992/0x1680
> notify_change+0x61a/0xa80
> utimes_common+0x3d4/0x870
> do_utimes+0x1c1/0x220
> SyS_utimensat+0x84/0x1a0
> entry_SYSCALL_64_fastpath+0x1f/0xbe
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&sb->s_type->i_mutex_key#11);
> lock(&cifsi->lock_sem);
> lock(&sb->s_type->i_mutex_key#11);
> lock(&cifsi->lock_sem);
>
> *** DEADLOCK ***
>
> 2 locks held by touch/487:
> #0: (sb_writers#10){.+.+.+}, at: mnt_want_write+0x41/0xb0
> #1: (&sb->s_type->i_mutex_key#11){+.+.+.}, at: utimes_common+0x3ad/0x870
>
> stack backtrace:
> CPU: 0 PID: 487 Comm: touch Not tainted 4.12.0-rc7+ #9
> Call Trace:
> dump_stack+0xdb/0x185
> print_circular_bug+0x45b/0x790
> __lock_acquire+0x1f74/0x38f0
> lock_acquire+0x1cc/0x600
> down_write+0x74/0x110
> cifsFileInfo_put+0x88f/0x16a0
> cifs_setattr+0x992/0x1680
> notify_change+0x61a/0xa80
> utimes_common+0x3d4/0x870
> do_utimes+0x1c1/0x220
> SyS_utimensat+0x84/0x1a0
> entry_SYSCALL_64_fastpath+0x1f/0xbe
>
> Fixes: 19dfc1f5f2ef03a52 ("cifs: fix the race in cifs_writev()")
> Signed-off-by: Rabin Vincent <rabinv@xxxxxxxx>
> ---
> fs/cifs/file.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index fcef706..d16fa55 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2810,12 +2810,12 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from)
> struct TCP_Server_Info *server = tlink_tcon(cfile->tlink)->ses->server;
> ssize_t rc;
>
> + inode_lock(inode);
> /*
> * We need to hold the sem to be sure nobody modifies lock list
> * with a brlock that prevents writing.
> */
> down_read(&cinode->lock_sem);
> - inode_lock(inode);
>
> rc = generic_write_checks(iocb, from);
> if (rc <= 0)
> @@ -2828,11 +2828,11 @@ cifs_writev(struct kiocb *iocb, struct iov_iter *from)
> else
> rc = -EACCES;
> out:
> + up_read(&cinode->lock_sem);
> inode_unlock(inode);
>
> if (rc > 0)
> rc = generic_write_sync(iocb, rc);
> - up_read(&cinode->lock_sem);
> return rc;
> }
>
> --
> 2.1.4
>
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Acked-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
--
Best regards,
Pavel Shilovsky
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