diff options
author | Hans de Goede <hdegoede@redhat.com> | 2020-07-24 19:47:01 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-07-29 14:11:05 +0200 |
commit | a37241d83465dbcb1981093e139701a0755156e3 (patch) | |
tree | 657c8951b9b6efd82d21644da2b58ae2ae138a09 /drivers/usb | |
parent | 95b4d51c96a87cd760c2a4f27fb28a59a27b6368 (diff) |
usb: typec: tcpm: Fix AB BA lock inversion between tcpm code and the alt-mode drivers
When we receive a PD data packet which ends up being for the alt-mode
driver we have the following lock order:
1. tcpm_pd_rx_handler take the tcpm-port lock
2. We call into the alt-mode driver which takes the alt-mode's lock
And when the alt-mode driver initiates communication we have the following
lock order:
3. alt-mode driver takes the alt-mode's lock
4. alt-mode driver calls tcpm_altmode_enter which takes the tcpm-port lock
This is a classic AB BA lock inversion issue.
With the refactoring of tcpm_handle_vdm_request() done before this patch,
we don't rely on, or need to make changes to the tcpm-port data by the
time we make call 2. from above. All data to be passed to the alt-mode
driver sits on our stack at this point, and thus does not need locking.
So after the refactoring we can simply fix this by releasing the
tcpm-port lock before calling into the alt-mode driver.
This fixes the following lockdep warning:
[ 191.454238] ======================================================
[ 191.454240] WARNING: possible circular locking dependency detected
[ 191.454244] 5.8.0-rc5+ #1 Not tainted
[ 191.454246] ------------------------------------------------------
[ 191.454248] kworker/u8:5/794 is trying to acquire lock:
[ 191.454251] ffff9bac8e30d4a8 (&dp->lock){+.+.}-{3:3}, at: dp_altmode_vdm+0x30/0xf0 [typec_displayport]
[ 191.454263]
but task is already holding lock:
[ 191.454264] ffff9bac9dc240a0 (&port->lock#2){+.+.}-{3:3}, at: tcpm_pd_rx_handler+0x43/0x12c0 [tcpm]
[ 191.454273]
which lock already depends on the new lock.
[ 191.454275]
the existing dependency chain (in reverse order) is:
[ 191.454277]
-> #1 (&port->lock#2){+.+.}-{3:3}:
[ 191.454286] __mutex_lock+0x7b/0x820
[ 191.454290] tcpm_altmode_enter+0x23/0x90 [tcpm]
[ 191.454293] dp_altmode_work+0xca/0xe0 [typec_displayport]
[ 191.454299] process_one_work+0x23f/0x570
[ 191.454302] worker_thread+0x55/0x3c0
[ 191.454305] kthread+0x138/0x160
[ 191.454309] ret_from_fork+0x22/0x30
[ 191.454311]
-> #0 (&dp->lock){+.+.}-{3:3}:
[ 191.454317] __lock_acquire+0x1241/0x2090
[ 191.454320] lock_acquire+0xa4/0x3d0
[ 191.454323] __mutex_lock+0x7b/0x820
[ 191.454326] dp_altmode_vdm+0x30/0xf0 [typec_displayport]
[ 191.454330] tcpm_pd_rx_handler+0x11ae/0x12c0 [tcpm]
[ 191.454333] process_one_work+0x23f/0x570
[ 191.454336] worker_thread+0x55/0x3c0
[ 191.454338] kthread+0x138/0x160
[ 191.454341] ret_from_fork+0x22/0x30
[ 191.454343]
other info that might help us debug this:
[ 191.454345] Possible unsafe locking scenario:
[ 191.454347] CPU0 CPU1
[ 191.454348] ---- ----
[ 191.454350] lock(&port->lock#2);
[ 191.454353] lock(&dp->lock);
[ 191.454355] lock(&port->lock#2);
[ 191.454357] lock(&dp->lock);
[ 191.454360]
*** DEADLOCK ***
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200724174702.61754-5-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb')
-rw-r--r-- | drivers/usb/typec/tcpm/tcpm.c | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c index 51400cce582e..87ed5e2f79ca 100644 --- a/drivers/usb/typec/tcpm/tcpm.c +++ b/drivers/usb/typec/tcpm/tcpm.c @@ -1251,6 +1251,27 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port, if (PD_VDO_SVDM(p[0])) rlen = tcpm_pd_svdm(port, adev, p, cnt, response, &adev_action); + /* + * We are done with any state stored in the port struct now, except + * for any port struct changes done by the tcpm_queue_vdm() call + * below, which is a separate operation. + * + * So we can safely release the lock here; and we MUST release the + * lock here to avoid an AB BA lock inversion: + * + * If we keep the lock here then the lock ordering in this path is: + * 1. tcpm_pd_rx_handler take the tcpm port lock + * 2. One of the typec_altmode_* calls below takes the alt-mode's lock + * + * And we also have this ordering: + * 1. alt-mode driver takes the alt-mode's lock + * 2. alt-mode driver calls tcpm_altmode_enter which takes the + * tcpm port lock + * + * Dropping our lock here avoids this. + */ + mutex_unlock(&port->lock); + if (adev) { switch (adev_action) { case ADEV_NONE: @@ -1275,6 +1296,15 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port, } } + /* + * We must re-take the lock here to balance the unlock in + * tcpm_pd_rx_handler, note that no changes, other then the + * tcpm_queue_vdm call, are made while the lock is held again. + * All that is done after the call is unwinding the call stack until + * we return to tcpm_pd_rx_handler and do the unlock there. + */ + mutex_lock(&port->lock); + if (rlen > 0) tcpm_queue_vdm(port, response[0], &response[1], rlen - 1); } |