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Subject[PATCH 2/5] nvme: don't hold nvmf_transports_rwsem for more than transport lookups
Date
Only take nvmf_transports_rwsem when doing a lookup of regitered
transports, as subsequent actions may take the hctx_lock which is an
rcu_read_lock and thus lockdep complains about suspicious rcu usage.

[ 9.703333] =============================
[ 9.704797] WARNING: suspicious RCU usage
[ 9.706250] 4.17.0-rc5+ #883 Not tainted
[ 9.708146] -----------------------------
[ 9.708868] ./include/linux/rcupdate.h:304 Illegal context switch in RCU read-side critical section!
[ 9.710511]
[ 9.710511] other info that might help us debug this:
[ 9.710511]
[ 9.711959]
[ 9.711959] rcu_scheduler_active = 2, debug_locks = 1
[ 9.713142] 3 locks held by nvme/1420:
[ 9.713800] #0: (ptrval) (nvmf_dev_mutex){+.+.}, at: nvmf_dev_write+0x6a/0xb7d [nvme_fabrics]
[ 9.715471] #1: (ptrval) (nvmf_transports_rwsem){++++}, at: nvmf_dev_write+0x6e5/0xb7d [nvme_fabrics]
[ 9.717279] #2: (ptrval) (rcu_read_lock){....}, at: hctx_lock+0x56/0xd0
[ 9.718636]
[ 9.718636] stack backtrace:
[ 9.720266] CPU: 2 PID: 1420 Comm: nvme Not tainted 4.17.0-rc5+ #883
[ 9.721446] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
[ 9.723003] Call Trace:
[ 9.723453] dump_stack+0x78/0xb3
[ 9.724059] ___might_sleep+0xde/0x250
[ 9.724749] kmem_cache_alloc_trace+0x1ae/0x270
[ 9.725565] fcloop_fcp_req+0x32/0x1a0 [nvme_fcloop]
[ 9.726428] nvme_fc_start_fcp_op.part.39+0x193/0x4c0 [nvme_fc]
[ 9.727425] blk_mq_dispatch_rq_list+0x7f/0x4a0
[ 9.728219] ? blk_mq_flush_busy_ctxs+0xa8/0xf0
[ 9.729035] blk_mq_sched_dispatch_requests+0x16e/0x170
[ 9.729984] __blk_mq_run_hw_queue+0x79/0xd0
[ 9.730737] __blk_mq_delay_run_hw_queue+0x11c/0x160
[ 9.731647] blk_mq_run_hw_queue+0x63/0xc0
[ 9.732357] blk_mq_sched_insert_request+0xb2/0x140
[ 9.733204] blk_execute_rq+0x64/0xc0
[ 9.733840] __nvme_submit_sync_cmd+0x63/0xd0 [nvme_core]
[ 9.734772] nvmf_connect_admin_queue+0x11e/0x190 [nvme_fabrics]
[ 9.735815] ? mark_held_locks+0x6b/0x90
[ 9.736504] nvme_fc_create_association+0x35b/0x970 [nvme_fc]
[ 9.737489] nvme_fc_create_ctrl+0x5d2/0x830 [nvme_fc]
[ 9.738379] nvmf_dev_write+0x92d/0xb7d [nvme_fabrics]
[ 9.739253] __vfs_write+0x21/0x130
[ 9.739895] ? selinux_file_permission+0xe9/0x140
[ 9.740698] ? security_file_permission+0x2f/0xb0
[ 9.741526] vfs_write+0xbd/0x1c0
[ 9.742095] ksys_write+0x40/0xa0
[ 9.742681] ? do_syscall_64+0xd/0x190
[ 9.743335] do_syscall_64+0x51/0x190
[ 9.744415] entry_SYSCALL_64_after_hwframe+0x49/0xbe

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
---
drivers/nvme/host/fabrics.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index 7ae732a77fe8..febf82639b40 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -957,16 +957,17 @@ nvmf_create_ctrl(struct device *dev, const char *buf, size_t count)

down_read(&nvmf_transports_rwsem);
ops = nvmf_lookup_transport(opts);
+ up_read(&nvmf_transports_rwsem);
if (!ops) {
pr_info("no handler found for transport %s.\n",
opts->transport);
ret = -EINVAL;
- goto out_unlock;
+ goto out_free_opts;
}

if (!try_module_get(ops->module)) {
ret = -EBUSY;
- goto out_unlock;
+ goto out_free_opts;
}

ret = nvmf_check_required_opts(opts, ops->required_opts);
@@ -988,19 +989,15 @@ nvmf_create_ctrl(struct device *dev, const char *buf, size_t count)
"controller returned incorrect NQN: \"%s\".\n",
ctrl->subsys->subnqn);
module_put(ops->module);
- up_read(&nvmf_transports_rwsem);
nvme_delete_ctrl_sync(ctrl);
return ERR_PTR(-EINVAL);
}

module_put(ops->module);
- up_read(&nvmf_transports_rwsem);
return ctrl;

out_module_put:
module_put(ops->module);
-out_unlock:
- up_read(&nvmf_transports_rwsem);
out_free_opts:
nvmf_free_options(opts);
return ERR_PTR(ret);
--
2.16.3
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