On Thu, Aug 29, 2019 at 09:42:31PM +0200, Martin Hundebøll wrote:
> On 22/08/2019 23.56, Martin Hundebøll wrote:
> > When tearing down the n_gsm ldisc while one or more of its child ports
> > are open, a lock dep warning occurs:
> >
> > [ 56.254258] ======================================================
> > [ 56.260447] WARNING: possible circular locking dependency detected
> > [ 56.266641] 5.2.0-00118-g1fd58e20e5b0 #30 Not tainted
> > [ 56.271701] ------------------------------------------------------
> > [ 56.277890] cmux/271 is trying to acquire lock:
> > [ 56.282436] 8215283a (&tty->legacy_mutex){+.+.}, at:
> > __tty_hangup.part.0+0x58/0x27c
> > [ 56.290128]
> > [ 56.290128] but task is already holding lock:
> > [ 56.295970] e9e2b842 (&gsm->mutex){+.+.}, at: gsm_cleanup_mux+0x9c/0x15c
> > [ 56.302699]
> > [ 56.302699] which lock already depends on the new lock.
> > [ 56.302699]
> > [ 56.310884]
> > [ 56.310884] the existing dependency chain (in reverse order) is:
> > [ 56.318372]
> > [ 56.318372] -> #2 (&gsm->mutex){+.+.}:
> > [ 56.323624] mutex_lock_nested+0x1c/0x24
> > [ 56.328079] gsm_cleanup_mux+0x9c/0x15c
> > [ 56.332448] gsmld_ioctl+0x418/0x4e8
> > [ 56.336554] tty_ioctl+0x96c/0xcb0
> > [ 56.340492] do_vfs_ioctl+0x41c/0xa5c
> > [ 56.344685] ksys_ioctl+0x34/0x60
> > [ 56.348535] ret_fast_syscall+0x0/0x28
> > [ 56.352815] 0xbe97cc04
> > [ 56.355791]
> > [ 56.355791] -> #1 (&tty->ldisc_sem){++++}:
> > [ 56.361388] tty_ldisc_lock+0x50/0x74
> > [ 56.365581] tty_init_dev+0x88/0x1c4
> > [ 56.369687] tty_open+0x1c8/0x430
> > [ 56.373536] chrdev_open+0xa8/0x19c
> > [ 56.377560] do_dentry_open+0x118/0x3c4
> > [ 56.381928] path_openat+0x2fc/0x1190
> > [ 56.386123] do_filp_open+0x68/0xd4
> > [ 56.390146] do_sys_open+0x164/0x220
> > [ 56.394257] kernel_init_freeable+0x328/0x3e4
> > [ 56.399146] kernel_init+0x8/0x110
> > [ 56.403078] ret_from_fork+0x14/0x20
> > [ 56.407183] 0x0
> > [ 56.409548]
> > [ 56.409548] -> #0 (&tty->legacy_mutex){+.+.}:
> > [ 56.415402] __mutex_lock+0x64/0x90c
> > [ 56.419508] mutex_lock_nested+0x1c/0x24
> > [ 56.423961] __tty_hangup.part.0+0x58/0x27c
> > [ 56.428676] gsm_cleanup_mux+0xe8/0x15c
> > [ 56.433043] gsmld_close+0x48/0x90
> > [ 56.436979] tty_ldisc_kill+0x2c/0x6c
> > [ 56.441173] tty_ldisc_release+0x88/0x194
> > [ 56.445715] tty_release_struct+0x14/0x44
> > [ 56.450254] tty_release+0x36c/0x43c
> > [ 56.454365] __fput+0x94/0x1e8
> >
> > Avoid the warning by doing the port hangup asynchronously.
>
> Any comments?
Sorry, was waiting to see if anyone would review this, I'll go do it
later today...
