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Date: Tue, 4 Mar 2014 18:50:16 -0800
From: Greg KH <greg@...ah.com>
To: Tejun Heo <tj@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH driver-core-next] kernfs: cache atomic_write_len in
kernfs_open_file
On Tue, Mar 04, 2014 at 03:38:46PM -0500, Tejun Heo wrote:
> While implementing atomic_write_len, 4d3773c4bb41 ("kernfs: implement
> kernfs_ops->atomic_write_len") moved data copy from userland inside
> kernfs_get_active() and kernfs_open_file->mutex so that
> kernfs_ops->atomic_write_len can be accessed before copying buffer
> from userland; unfortunately, this could lead to locking order
> inversion involving mmap_sem if copy_from_user() takes a page fault.
>
> ======================================================
> [ INFO: possible circular locking dependency detected ]
> 3.14.0-rc4-next-20140228-sasha-00011-g4077c67-dirty #26 Tainted: G W
> -------------------------------------------------------
> trinity-c236/10658 is trying to acquire lock:
> (&of->mutex#2){+.+.+.}, at: [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
>
> but task is already holding lock:
> (&mm->mmap_sem){++++++}, at: [<mm/util.c:397>] vm_mmap_pgoff+0x6e/0xe0
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&mm->mmap_sem){++++++}:
> [<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
> [<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
> [<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
> [<mm/memory.c:4188>] might_fault+0x7e/0xb0
> [<arch/x86/include/asm/uaccess.h:713 fs/kernfs/file.c:291>] kernfs_fop_write+0xd8/0x190
> [<fs/read_write.c:473>] vfs_write+0xe3/0x1d0
> [<fs/read_write.c:523 fs/read_write.c:515>] SyS_write+0x5d/0xa0
> [<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
>
> -> #0 (&of->mutex#2){+.+.+.}:
> [<kernel/locking/lockdep.c:1840>] check_prev_add+0x13f/0x560
> [<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
> [<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
> [<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
> [<kernel/locking/mutex.c:470 kernel/locking/mutex.c:571>] mutex_lock_nested+0x6a/0x510
> [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
> [<mm/mmap.c:1573>] mmap_region+0x310/0x5c0
> [<mm/mmap.c:1365>] do_mmap_pgoff+0x385/0x430
> [<mm/util.c:399>] vm_mmap_pgoff+0x8f/0xe0
> [<mm/mmap.c:1416 mm/mmap.c:1374>] SyS_mmap_pgoff+0x1b0/0x210
> [<arch/x86/kernel/sys_x86_64.c:72>] SyS_mmap+0x1d/0x20
> [<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&mm->mmap_sem);
> lock(&of->mutex#2);
> lock(&mm->mmap_sem);
> lock(&of->mutex#2);
>
> *** DEADLOCK ***
>
> 1 lock held by trinity-c236/10658:
> #0: (&mm->mmap_sem){++++++}, at: [<mm/util.c:397>] vm_mmap_pgoff+0x6e/0xe0
>
> stack backtrace:
> CPU: 2 PID: 10658 Comm: trinity-c236 Tainted: G W 3.14.0-rc4-next-20140228-sasha-00011-g4077c67-dirty #26
> 0000000000000000 ffff88011911fa48 ffffffff8438e945 0000000000000000
> 0000000000000000 ffff88011911fa98 ffffffff811a0109 ffff88011911fab8
> ffff88011911fab8 ffff88011911fa98 ffff880119128cc0 ffff880119128cf8
> Call Trace:
> [<lib/dump_stack.c:52>] dump_stack+0x52/0x7f
> [<kernel/locking/lockdep.c:1213>] print_circular_bug+0x129/0x160
> [<kernel/locking/lockdep.c:1840>] check_prev_add+0x13f/0x560
> [<include/linux/spinlock.h:343 mm/slub.c:1933>] ? deactivate_slab+0x511/0x550
> [<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
> [<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
> [<mm/mmap.c:1552>] ? mmap_region+0x24a/0x5c0
> [<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
> [<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
> [<kernel/locking/mutex.c:470 kernel/locking/mutex.c:571>] mutex_lock_nested+0x6a/0x510
> [<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
> [<kernel/sched/core.c:2477>] ? get_parent_ip+0x11/0x50
> [<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
> [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
> [<mm/mmap.c:1573>] mmap_region+0x310/0x5c0
> [<mm/mmap.c:1365>] do_mmap_pgoff+0x385/0x430
> [<mm/util.c:397>] ? vm_mmap_pgoff+0x6e/0xe0
> [<mm/util.c:399>] vm_mmap_pgoff+0x8f/0xe0
> [<kernel/rcu/update.c:97>] ? __rcu_read_unlock+0x44/0xb0
> [<fs/file.c:641>] ? dup_fd+0x3c0/0x3c0
> [<mm/mmap.c:1416 mm/mmap.c:1374>] SyS_mmap_pgoff+0x1b0/0x210
> [<arch/x86/kernel/sys_x86_64.c:72>] SyS_mmap+0x1d/0x20
> [<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
>
> Fix it by caching atomic_write_len in kernfs_open_file during open so
> that it can be determined without accessing kernfs_ops in
> kernfs_fop_write(). This restores the structure of kernfs_fop_write()
> before 4d3773c4bb41 with updated @len determination logic.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Sasha Levin <sasha.levin@...cle.com>
> References: http://lkml.kernel.org/g/53113485.2090407@oracle.com
> ---
> fs/kernfs/file.c | 63 ++++++++++++++++++++++++-------------------------
> include/linux/kernfs.h | 1
> 2 files changed, 33 insertions(+), 31 deletions(-)
This is for 3.15, right?
thanks,
greg k-h
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