Messages in this thread Patch in this message |  | | Date | Tue, 21 Nov 2006 01:21:19 +0100 (CET) | From | Stefan Richter <> | Subject | Re: deadlock in "modprobe -r ohci1394" shortly after "modprobe ohci1394" |
| |
On 20 Nov, Alan Stern wrote: >> > Is the problem caused by the fact that some of these struct device's >> > aren't bound to a driver? Remember, bus_rescan_devices() will skip over >> > anything that already has a driver. Could you solve your problem by >> > adding a do_nothing driver that would bind to these otherwise unused >> > devices?
There are three minor problems with this approach: - some ballast in system memory for the dummy driver struct - the dummy driver is visible in sysfs - the (root) user can unbind the driver which will recreate the preconditions for the deadlock
Nevertheless, here is the patch. I find it ugly, maybe even more so than my previous up(&dev->parent->sem) hack, but it works as you said.
From: Stefan Richter <stefanr@s5r6.in-berlin.de> Subject: ieee1394: nodemgr: fix deadlock in shutdown
If "modprobe ohci1394" was quickly followed by "modprobe -r ohci1394", say with 1 second pause in between, the modprobe -r got stuck in uninterruptible sleep in kthread_stop. At the same time the knodemgrd slept uninterruptibly in bus_rescan_devices_helper.
This was a regression since Linux 2.6.16, commit bf74ad5bc41727d5f2f1c6bedb2c1fac394de731 "Hold the device's parent's lock during probe and remove"
The fix (or rather workaround) adds a dummy driver to the hpsb_host device. Now bus_rescan_devices_helper won't scan it anymore. This doesn't hurt since we have no drivers which will bind to these devices and it is unlikely that there will ever be such a driver.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> --- drivers/ieee1394/nodemgr.c | 19 ++++++++++++++++--- 1 files changed, 16 insertions(+), 3 deletions(-)
Index: linux-2.6.19-rc4/drivers/ieee1394/nodemgr.c =================================================================== --- linux-2.6.19-rc4.orig/drivers/ieee1394/nodemgr.c 2006-11-21 00:09:25.000000000 +0100 +++ linux-2.6.19-rc4/drivers/ieee1394/nodemgr.c 2006-11-21 01:00:28.000000000 +0100 @@ -259,9 +259,19 @@ static struct device nodemgr_dev_templat .release = nodemgr_release_ne, }; +/* The dummy driver prevents the host devices from being scanned. We have no + * useful drivers for them yet, and there is a deadlock possible if the driver + * core scans the host device while the host's low-level driver, i.e. the host's + * parent device, is being removed. */ +static struct device_driver nodemgr_dev_dummy_driver = { + .bus = &ieee1394_bus_type, + .name = "none", +}; + struct device nodemgr_dev_template_host = { .bus = &ieee1394_bus_type, .release = nodemgr_release_host, + .driver = &nodemgr_dev_dummy_driver, }; @@ -703,12 +713,15 @@ static int nodemgr_bus_match(struct devi if (dev->platform_data != &nodemgr_ud_platform_data) return 0; - ud = container_of(dev, struct unit_directory, device); - driver = container_of(drv, struct hpsb_protocol_driver, driver); + /* The dummy driver is not wrapped in a hpsb_protocol_driver */ + if (drv == &nodemgr_dev_dummy_driver) + return 0; + ud = container_of(dev, struct unit_directory, device); if (ud->ne->in_limbo || ud->ignore_driver) return 0; + driver = container_of(drv, struct hpsb_protocol_driver, driver); for (id = driver->id_table; id->match_flags != 0; id++) { if ((id->match_flags & IEEE1394_MATCH_VENDOR_ID) && id->vendor_id != ud->vendor_id) @@ -1899,7 +1912,7 @@ int init_ieee1394_nodemgr(void) class_unregister(&nodemgr_ne_class); return error; } - + error = driver_register(&nodemgr_dev_dummy_driver); hpsb_register_highlevel(&nodemgr_highlevel); return 0; }
-- Stefan Richter -=====-=-==- =-== =-=-= http://arcgraph.de/sr/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |