--- /dev/null
+From c7de87ff9dac5f396f62d584f3908f80ddc0e07b Mon Sep 17 00:00:00 2001
+From: Joe Korty <joe.korty@concurrent-rt.com>
+Date: Fri, 26 Feb 2021 09:38:20 -0500
+Subject: NFSD: Repair misuse of sv_lock in 5.10.16-rt30.
+
+From: Joe Korty <joe.korty@concurrent-rt.com>
+
+commit c7de87ff9dac5f396f62d584f3908f80ddc0e07b upstream.
+
+[ This problem is in mainline, but only rt has the chops to be
+able to detect it. ]
+
+Lockdep reports a circular lock dependency between serv->sv_lock and
+softirq_ctl.lock on system shutdown, when using a kernel built with
+CONFIG_PREEMPT_RT=y, and a nfs mount exists.
+
+This is due to the definition of spin_lock_bh on rt:
+
+ local_bh_disable();
+ rt_spin_lock(lock);
+
+which forces a softirq_ctl.lock -> serv->sv_lock dependency. This is
+not a problem as long as _every_ lock of serv->sv_lock is a:
+
+ spin_lock_bh(&serv->sv_lock);
+
+but there is one of the form:
+
+ spin_lock(&serv->sv_lock);
+
+This is what is causing the circular dependency splat. The spin_lock()
+grabs the lock without first grabbing softirq_ctl.lock via local_bh_disable.
+If later on in the critical region, someone does a local_bh_disable, we
+get a serv->sv_lock -> softirq_ctrl.lock dependency established. Deadlock.
+
+Fix is to make serv->sv_lock be locked with spin_lock_bh everywhere, no
+exceptions.
+
+[ OK ] Stopped target NFS client services.
+ Stopping Logout off all iSCSI sessions on shutdown...
+ Stopping NFS server and services...
+[ 109.442380]
+[ 109.442385] ======================================================
+[ 109.442386] WARNING: possible circular locking dependency detected
+[ 109.442387] 5.10.16-rt30 #1 Not tainted
+[ 109.442389] ------------------------------------------------------
+[ 109.442390] nfsd/1032 is trying to acquire lock:
+[ 109.442392] ffff994237617f60 ((softirq_ctrl.lock).lock){+.+.}-{2:2}, at: __local_bh_disable_ip+0xd9/0x270
+[ 109.442405]
+[ 109.442405] but task is already holding lock:
+[ 109.442406] ffff994245cb00b0 (&serv->sv_lock){+.+.}-{0:0}, at: svc_close_list+0x1f/0x90
+[ 109.442415]
+[ 109.442415] which lock already depends on the new lock.
+[ 109.442415]
+[ 109.442416]
+[ 109.442416] the existing dependency chain (in reverse order) is:
+[ 109.442417]
+[ 109.442417] -> #1 (&serv->sv_lock){+.+.}-{0:0}:
+[ 109.442421] rt_spin_lock+0x2b/0xc0
+[ 109.442428] svc_add_new_perm_xprt+0x42/0xa0
+[ 109.442430] svc_addsock+0x135/0x220
+[ 109.442434] write_ports+0x4b3/0x620
+[ 109.442438] nfsctl_transaction_write+0x45/0x80
+[ 109.442440] vfs_write+0xff/0x420
+[ 109.442444] ksys_write+0x4f/0xc0
+[ 109.442446] do_syscall_64+0x33/0x40
+[ 109.442450] entry_SYSCALL_64_after_hwframe+0x44/0xa9
+[ 109.442454]
+[ 109.442454] -> #0 ((softirq_ctrl.lock).lock){+.+.}-{2:2}:
+[ 109.442457] __lock_acquire+0x1264/0x20b0
+[ 109.442463] lock_acquire+0xc2/0x400
+[ 109.442466] rt_spin_lock+0x2b/0xc0
+[ 109.442469] __local_bh_disable_ip+0xd9/0x270
+[ 109.442471] svc_xprt_do_enqueue+0xc0/0x4d0
+[ 109.442474] svc_close_list+0x60/0x90
+[ 109.442476] svc_close_net+0x49/0x1a0
+[ 109.442478] svc_shutdown_net+0x12/0x40
+[ 109.442480] nfsd_destroy+0xc5/0x180
+[ 109.442482] nfsd+0x1bc/0x270
+[ 109.442483] kthread+0x194/0x1b0
+[ 109.442487] ret_from_fork+0x22/0x30
+[ 109.442492]
+[ 109.442492] other info that might help us debug this:
+[ 109.442492]
+[ 109.442493] Possible unsafe locking scenario:
+[ 109.442493]
+[ 109.442493] CPU0 CPU1
+[ 109.442494] ---- ----
+[ 109.442495] lock(&serv->sv_lock);
+[ 109.442496] lock((softirq_ctrl.lock).lock);
+[ 109.442498] lock(&serv->sv_lock);
+[ 109.442499] lock((softirq_ctrl.lock).lock);
+[ 109.442501]
+[ 109.442501] *** DEADLOCK ***
+[ 109.442501]
+[ 109.442501] 3 locks held by nfsd/1032:
+[ 109.442503] #0: ffffffff93b49258 (nfsd_mutex){+.+.}-{3:3}, at: nfsd+0x19a/0x270
+[ 109.442508] #1: ffff994245cb00b0 (&serv->sv_lock){+.+.}-{0:0}, at: svc_close_list+0x1f/0x90
+[ 109.442512] #2: ffffffff93a81b20 (rcu_read_lock){....}-{1:2}, at: rt_spin_lock+0x5/0xc0
+[ 109.442518]
+[ 109.442518] stack backtrace:
+[ 109.442519] CPU: 0 PID: 1032 Comm: nfsd Not tainted 5.10.16-rt30 #1
+[ 109.442522] Hardware name: Supermicro X9DRL-3F/iF/X9DRL-3F/iF, BIOS 3.2 09/22/2015
+[ 109.442524] Call Trace:
+[ 109.442527] dump_stack+0x77/0x97
+[ 109.442533] check_noncircular+0xdc/0xf0
+[ 109.442546] __lock_acquire+0x1264/0x20b0
+[ 109.442553] lock_acquire+0xc2/0x400
+[ 109.442564] rt_spin_lock+0x2b/0xc0
+[ 109.442570] __local_bh_disable_ip+0xd9/0x270
+[ 109.442573] svc_xprt_do_enqueue+0xc0/0x4d0
+[ 109.442577] svc_close_list+0x60/0x90
+[ 109.442581] svc_close_net+0x49/0x1a0
+[ 109.442585] svc_shutdown_net+0x12/0x40
+[ 109.442588] nfsd_destroy+0xc5/0x180
+[ 109.442590] nfsd+0x1bc/0x270
+[ 109.442595] kthread+0x194/0x1b0
+[ 109.442600] ret_from_fork+0x22/0x30
+[ 109.518225] nfsd: last server has exited, flushing export cache
+[ OK ] Stopped NFSv4 ID-name mapping service.
+[ OK ] Stopped GSSAPI Proxy Daemon.
+[ OK ] Stopped NFS Mount Daemon.
+[ OK ] Stopped NFS status monitor for NFSv2/3 locking..
+
+Fixes: 719f8bcc883e ("svcrpc: fix xpt_list traversal locking on shutdown")
+Signed-off-by: Joe Korty <joe.korty@concurrent-rt.com>
+Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ net/sunrpc/svc_xprt.c | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+--- a/net/sunrpc/svc_xprt.c
++++ b/net/sunrpc/svc_xprt.c
+@@ -1011,7 +1011,7 @@ static int svc_close_list(struct svc_ser
+ struct svc_xprt *xprt;
+ int ret = 0;
+
+- spin_lock(&serv->sv_lock);
++ spin_lock_bh(&serv->sv_lock);
+ list_for_each_entry(xprt, xprt_list, xpt_list) {
+ if (xprt->xpt_net != net)
+ continue;
+@@ -1019,7 +1019,7 @@ static int svc_close_list(struct svc_ser
+ set_bit(XPT_CLOSE, &xprt->xpt_flags);
+ svc_xprt_enqueue(xprt);
+ }
+- spin_unlock(&serv->sv_lock);
++ spin_unlock_bh(&serv->sv_lock);
+ return ret;
+ }
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
