Messages in this thread Patch in this message | | | Date | Sun, 10 Jul 2022 11:25:08 +0900 | Subject | [PATCH v2 3/4] PM: hibernate: allow wait_for_device_probe() to timeout when resuming from hibernation | From | Tetsuo Handa <> |
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syzbot is reporting hung task at misc_open() [1], for there is a race window of AB-BA deadlock which involves probe_count variable.
Even with "char: misc: allow calling open() callback without misc_mtx held" and "PM: hibernate: call wait_for_device_probe() without system_transition_mutex held", wait_for_device_probe() from snapshot_open() can sleep forever if probe_count cannot become 0.
Since snapshot_open() is a userland-driven hibernation/resume request, it should be acceptable to fail if something is wrong. Users would not want to wait for hours if device stopped responding. Therefore, introduce killable version of wait_for_device_probe() with timeout.
According to Oliver Neukum, there are SCSI commands that can run for more than 60 seconds. Therefore, this patch choose 5 minutes for timeout.
Link: https://syzkaller.appspot.com/bug?extid=358c9ab4c93da7b7238c [1] Reported-by: syzbot <syzbot+358c9ab4c93da7b7238c@syzkaller.appspotmail.com> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: Oliver Neukum <oneukum@suse.com> Cc: Wedson Almeida Filho <wedsonaf@google.com> Cc: Rafael J. Wysocki <rjw@sisk.pl> Cc: Arjan van de Ven <arjan@linux.intel.com> --- drivers/base/dd.c | 14 ++++++++++++++ include/linux/device/driver.h | 1 + kernel/power/user.c | 9 +++++++-- 3 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/drivers/base/dd.c b/drivers/base/dd.c index 70f79fc71539..3136b8403bb0 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -724,6 +724,20 @@ void wait_for_device_probe(void) } EXPORT_SYMBOL_GPL(wait_for_device_probe); +void wait_for_device_probe_killable_timeout(unsigned long timeout) +{ + /* wait for probe timeout */ + wait_event(probe_timeout_waitqueue, !driver_deferred_probe_timeout); + + /* wait for the deferred probe workqueue to finish */ + flush_work(&deferred_probe_work); + + /* wait for the known devices to complete their probing */ + wait_event_killable_timeout(probe_waitqueue, + atomic_read(&probe_count) == 0, timeout); + async_synchronize_full(); +} + static int __driver_probe_device(struct device_driver *drv, struct device *dev) { int ret = 0; diff --git a/include/linux/device/driver.h b/include/linux/device/driver.h index 7acaabde5396..4ee909144470 100644 --- a/include/linux/device/driver.h +++ b/include/linux/device/driver.h @@ -129,6 +129,7 @@ extern struct device_driver *driver_find(const char *name, struct bus_type *bus); extern int driver_probe_done(void); extern void wait_for_device_probe(void); +extern void wait_for_device_probe_killable_timeout(unsigned long timeout); void __init wait_for_init_devices_probe(void); /* sysfs interface for exporting driver attributes */ diff --git a/kernel/power/user.c b/kernel/power/user.c index db98a028dfdd..32dd5a855e8c 100644 --- a/kernel/power/user.c +++ b/kernel/power/user.c @@ -58,8 +58,13 @@ static int snapshot_open(struct inode *inode, struct file *filp) /* The image device should be already ready. */ break; default: /* Resuming */ - /* We may need to wait for the image device to appear. */ - wait_for_device_probe(); + /* + * Since the image device might not be ready, try to wait up to + * 5 minutes. We should not wait forever, for we might get stuck + * due to unresponsive devices and/or new probe events which + * are irrelevant to the image device keep coming in. + */ + wait_for_device_probe_killable_timeout(300 * HZ); break; } -- 2.18.4
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