| From c749d8c018daf5fba6dfac7b6c5c78b27efd7d65 Mon Sep 17 00:00:00 2001 |
| From: Vineeth Vijayan <vneethv@linux.ibm.com> |
| Date: Wed, 9 Jun 2021 09:21:08 +0200 |
| Subject: s390/cio: dont call css_wait_for_slow_path() inside a lock |
| |
| From: Vineeth Vijayan <vneethv@linux.ibm.com> |
| |
| commit c749d8c018daf5fba6dfac7b6c5c78b27efd7d65 upstream. |
| |
| Currently css_wait_for_slow_path() gets called inside the chp->lock. |
| The path-verification-loop of slowpath inside this lock could lead to |
| deadlock as reported by the lockdep validator. |
| |
| The ccw_device_get_chp_desc() during the instance of a device-set-online |
| would try to acquire the same 'chp->lock' to read the chp->desc. |
| The instance of this function can get called from multiple scenario, |
| like probing or setting-device online manually. This could, in some |
| corner-cases lead to the deadlock. |
| |
| lockdep validator reported this as, |
| |
| CPU0 CPU1 |
| ---- ---- |
| lock(&chp->lock); |
| lock(kn->active#43); |
| lock(&chp->lock); |
| lock((wq_completion)cio); |
| |
| The chp->lock was introduced to serialize the access of struct |
| channel_path. This lock is not needed for the css_wait_for_slow_path() |
| function, so invoke the slow-path function outside this lock. |
| |
| Fixes: b730f3a93395 ("[S390] cio: add lock to struct channel_path") |
| Cc: <stable@vger.kernel.org> |
| Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com> |
| Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com> |
| Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/s390/cio/chp.c | 3 +++ |
| drivers/s390/cio/chsc.c | 2 -- |
| 2 files changed, 3 insertions(+), 2 deletions(-) |
| |
| --- a/drivers/s390/cio/chp.c |
| +++ b/drivers/s390/cio/chp.c |
| @@ -255,6 +255,9 @@ static ssize_t chp_status_write(struct d |
| if (!num_args) |
| return count; |
| |
| + /* Wait until previous actions have settled. */ |
| + css_wait_for_slow_path(); |
| + |
| if (!strncasecmp(cmd, "on", 2) || !strcmp(cmd, "1")) { |
| mutex_lock(&cp->lock); |
| error = s390_vary_chpid(cp->chpid, 1); |
| --- a/drivers/s390/cio/chsc.c |
| +++ b/drivers/s390/cio/chsc.c |
| @@ -757,8 +757,6 @@ int chsc_chp_vary(struct chp_id chpid, i |
| { |
| struct channel_path *chp = chpid_to_chp(chpid); |
| |
| - /* Wait until previous actions have settled. */ |
| - css_wait_for_slow_path(); |
| /* |
| * Redo PathVerification on the devices the chpid connects to |
| */ |