The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8aac0e2338916e273ccbd438a2b7a1e8c61749f5 Mon Sep 17 00:00:00 2001

From: Dan Williams dan.j.williams@intel.com Date: Wed, 17 Jul 2019 18:07:58 -0700 Subject: [PATCH] libnvdimm/bus: Prevent duplicate device_unregister() calls

A multithreaded namespace creation/destruction stress test currently fails with signatures like the following:

sysfs group 'power' not found for kobject 'dax1.1' RIP: 0010:sysfs_remove_group+0x76/0x80 Call Trace: device_del+0x73/0x370 device_unregister+0x16/0x50 nd_async_device_unregister+0x1e/0x30 [libnvdimm] async_run_entry_fn+0x39/0x160 process_one_work+0x23c/0x5e0 worker_thread+0x3c/0x390

BUG: kernel NULL pointer dereference, address: 0000000000000020 RIP: 0010:klist_put+0x1b/0x6c Call Trace: klist_del+0xe/0x10 device_del+0x8a/0x2c9 ? __switch_to_asm+0x34/0x70 ? __switch_to_asm+0x40/0x70 device_unregister+0x44/0x4f nd_async_device_unregister+0x22/0x2d [libnvdimm] async_run_entry_fn+0x47/0x15a process_one_work+0x1a2/0x2eb worker_thread+0x1b8/0x26e

Use the kill_device() helper to atomically resolve the race of multiple threads issuing kill, device_unregister(), requests.

Reported-by: Jane Chu jane.chu@oracle.com Reported-by: Erwin Tsaur erwin.tsaur@oracle.com Fixes: 4d88a97aa9e8 ("libnvdimm, nvdimm: dimm driver and base libnvdimm device-driver...") Cc: stable@vger.kernel.org Link: https://github.com/pmem/ndctl/issues/96 Tested-by: Tested-by: Jane Chu jane.chu@oracle.com Link: https://lore.kernel.org/r/156341207846.292348.10435719262819764054.stgit@dwi... Signed-off-by: Dan Williams dan.j.williams@intel.com

diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c index 2dca3034fee0..42713b210f51 100644 --- a/drivers/nvdimm/bus.c +++ b/drivers/nvdimm/bus.c @@ -547,13 +547,38 @@ EXPORT_SYMBOL(nd_device_register);

void nd_device_unregister(struct device *dev, enum nd_async_mode mode) { + bool killed; + switch (mode) { case ND_ASYNC: + /* + * In the async case this is being triggered with the + * device lock held and the unregistration work needs to + * be moved out of line iff this is thread has won the + * race to schedule the deletion. + */ + if (!kill_device(dev)) + return; + get_device(dev); async_schedule_domain(nd_async_device_unregister, dev, &nd_async_domain); break; case ND_SYNC: + /* + * In the sync case the device is being unregistered due + * to a state change of the parent. Claim the kill state + * to synchronize against other unregistration requests, + * or otherwise let the async path handle it if the + * unregistration was already queued. + */ + device_lock(dev); + killed = kill_device(dev); + device_unlock(dev); + + if (!killed) + return; + nd_synchronize(); device_unregister(dev); break;