Messages in this thread Patch in this message | | | From | Johannes Thumshirn <> | Subject | [PATCH v3] nvme: fix lockdep warning in nvme_mpath_clear_current_path | Date | Thu, 17 May 2018 13:52:50 +0200 |
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When running blktest's nvme/005 with a lockdep enabled kernel the test case fails due to the following lockdep splat in dmesg:
============================= WARNING: suspicious RCU usage 4.17.0-rc5 #881 Not tainted ----------------------------- drivers/nvme/host/nvme.h:457 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 3 locks held by kworker/u32:5/1102: #0: (ptrval) ((wq_completion)"nvme-wq"){+.+.}, at: process_one_work+0x152/0x5c0 #1: (ptrval) ((work_completion)(&ctrl->scan_work)){+.+.}, at: process_one_work+0x152/0x5c0 #2: (ptrval) (&subsys->lock#2){+.+.}, at: nvme_ns_remove+0x43/0x1c0 [nvme_core]
The only caller of nvme_mpath_clear_current_path() is nvme_ns_remove() which holds the subsys lock so it's likely a false positive, but when using rcu_access_pointer(), we're telling rcu and lockdep that we're only after the pointer falue.
Fixes: 32acab3181c7 ("nvme: implement multipath access to nvme subsystems") Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de> Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
--- Changes to v2: - Added Christoph's R-b - Removed most of the lockdep splat from commit log
Changes to v1: - Change rcu_dereference_protected() to rc_access_pointer() (Paul)
--- drivers/nvme/host/nvme.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index 17d2f7cf3fed..af2bb6bc984d 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -22,6 +22,7 @@ #include <linux/lightnvm.h> #include <linux/sed-opal.h> #include <linux/fault-inject.h> +#include <linux/rcupdate.h> extern unsigned int nvme_io_timeout; #define NVME_IO_TIMEOUT (nvme_io_timeout * HZ) @@ -454,7 +455,7 @@ static inline void nvme_mpath_clear_current_path(struct nvme_ns *ns) { struct nvme_ns_head *head = ns->head; - if (head && ns == srcu_dereference(head->current_path, &head->srcu)) + if (head && ns == rcu_access_pointer(head->current_path)) rcu_assign_pointer(head->current_path, NULL); } struct nvme_ns *nvme_find_path(struct nvme_ns_head *head); -- 2.16.3
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