Commits
Martin Hundebøll committed 7030082a741
tty: n_gsm: avoid recursive locking with async port hangup
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.
Signed-off-by: Martin Hundebøll <martin@geanix.com>
Link: https://lore.kernel.org/r/20190822215601.9028-1-martin@geanix.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>