Re: [PATCH] padata: fix lockdep warning in padata serialization

[Daniel Jordan <daniel.m.jordan@oracle.com>]

On Mon, Sep 19, 2022 at 11:12:48AM -0400, Daniel Jordan wrote:
> Hi Edward,
> 
> On Mon, Sep 19, 2022 at 09:05:55AM +0800, eadavis@sina.com wrote:
> > From: Edward Adam Davis <eadavis@sina.com>
> > 
> > Parallelized object serialization uses spin_unlock for unlocking a spin lock
> > that was previously locked with spin_lock.
> 
> There's nothing unusual about that, though?
> 
> > This caused the following lockdep warning about an inconsistent lock
> > state:
> > 
> >         inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> 
> Neither HARDIRQ-ON-W nor IN-HARDIRQ-W appear in the syzbot report, did
> you mean SOFTIRQ-ON-W and IN-SOFTIRQ-W?
> 
> > We must use spin_lock_irqsave, because it is possible to trigger tipc 
> > from an irq handler.
> 
> A softirq handler, not a hardirq handler.  I'd suggest using
> spin_lock_bh() instead of _irqsave in your patch.
> 
> 
> A Fixes tag would be helpful for stable and folks backporting this fix
> to understand what kernel versions are affected.
> 
> > WARNING: inconsistent lock state
> > 6.0.0-rc5-syzkaller-00025-g3245cb65fd91 #0 Not tainted
> > --------------------------------
> > inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> > syz-executor.2/27685 [HC0[0]:SC1[1]:HE1:SE0] takes:
> > ffffe8ffffc7d280 (&pd_list->lock){+.?.}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
> > ffffe8ffffc7d280 (&pd_list->lock){+.?.}-{2:2}, at: padata_do_serial+0x21e/0x4b0 kernel/padata.c:392
> > {SOFTIRQ-ON-W} state was registered at:
> >   lock_acquire kernel/locking/lockdep.c:5666 [inline]
> >   lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
> >   __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
> >   _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
> >   spin_lock include/linux/spinlock.h:349 [inline]
> >   padata_do_serial+0x21e/0x4b0 kernel/padata.c:392
> >   pcrypt_aead_enc+0x57/0x70 crypto/pcrypt.c:89
> >   padata_do_parallel+0x87b/0xa10 kernel/padata.c:217
> >   pcrypt_aead_encrypt+0x39f/0x4d0 crypto/pcrypt.c:117
> >   crypto_aead_encrypt+0xaa/0xf0 crypto/aead.c:94
> >   tls_do_encryption net/tls/tls_sw.c:529 [inline]
> >   tls_push_record+0x13e8/0x3260 net/tls/tls_sw.c:762
> >   bpf_exec_tx_verdict+0xd82/0x11a0 net/tls/tls_sw.c:802
> >   tls_sw_sendmsg+0xa62/0x1820 net/tls/tls_sw.c:1014
> >   inet6_sendmsg+0x99/0xe0 net/ipv6/af_inet6.c:653
> >   sock_sendmsg_nosec net/socket.c:714 [inline]
> >   sock_sendmsg+0xcf/0x120 net/socket.c:734
> >   sock_write_iter+0x291/0x3d0 net/socket.c:1108
> >   call_write_iter include/linux/fs.h:2187 [inline]
> >   new_sync_write fs/read_write.c:491 [inline]
> >   vfs_write+0x9e9/0xdd0 fs/read_write.c:578
> >   ksys_write+0x1e8/0x250 fs/read_write.c:631
> >   do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
> >   __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
> >   do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203
> >   entry_SYSENTER_compat_after_hwframe+0x70/0x82
> > irq event stamp: 740
> > hardirqs last  enabled at (740): [<ffffffff814919a0>] __local_bh_enable_ip+0xa0/0x120 kernel/softirq.c:401
> > hardirqs last disabled at (739): [<ffffffff814919c3>] __local_bh_enable_ip+0xc3/0x120 kernel/softirq.c:378
> > softirqs last  enabled at (0): [<ffffffff8146f02e>] copy_process+0x213e/0x7090 kernel/fork.c:2202
> > softirqs last disabled at (717): [<ffffffff81491843>] invoke_softirq kernel/softirq.c:445 [inline]
> > softirqs last disabled at (717): [<ffffffff81491843>] __irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
> > 
> > other info that might help us debug this:
> >  Possible unsafe locking scenario:
> > 
> >        CPU0
> >        ----
> >   lock(&pd_list->lock);
> >   <Interrupt>
> >     lock(&pd_list->lock);
> > 
> >  *** DEADLOCK ***
> > 
> > 4 locks held by syz-executor.2/27685:
> >  #0: ffff8880445f0460 (sb_writers#3){.+.+}-{0:0}, at: open_last_lookups fs/namei.c:3470 [inline]
> >  #0: ffff8880445f0460 (sb_writers#3){.+.+}-{0:0}, at: path_openat+0x2613/0x28f0 fs/namei.c:3688
> >  #1: ffff8880465111a0 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:766 [inline]
> >  #1: ffff8880465111a0 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: open_last_lookups fs/namei.c:3480 [inline]
> >  #1: ffff8880465111a0 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: path_openat+0x1514/0x28f0 fs/namei.c:3688
> >  #2: ffffc900001e0d70 ((&d->timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:31 [inline]
> >  #2: ffffc900001e0d70 ((&d->timer)){+.-.}-{0:0}, at: call_timer_fn+0xd5/0x6b0 kernel/time/timer.c:1464
> >  #3: ffffffff8bf89400 (rcu_read_lock){....}-{1:2}, at: buf_msg net/tipc/msg.h:202 [inline]
> >  #3: ffffffff8bf89400 (rcu_read_lock){....}-{1:2}, at: tipc_bearer_xmit_skb+0x8c/0x410 net/tipc/bearer.c:550
> > 
> > stack backtrace:
> > CPU: 1 PID: 27685 Comm: syz-executor.2 Not tainted 6.0.0-rc5-syzkaller-00025-g3245cb65fd91 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
> > Call Trace:
> >  <IRQ>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
> >  print_usage_bug kernel/locking/lockdep.c:3961 [inline]
> >  valid_state kernel/locking/lockdep.c:3973 [inline]
> >  mark_lock_irq kernel/locking/lockdep.c:4176 [inline]
> >  mark_lock.part.0.cold+0x18/0xd8 kernel/locking/lockdep.c:4632
> >  mark_lock kernel/locking/lockdep.c:4596 [inline]
> >  mark_usage kernel/locking/lockdep.c:4527 [inline]
> >  __lock_acquire+0x11d9/0x56d0 kernel/locking/lockdep.c:5007
> >  lock_acquire kernel/locking/lockdep.c:5666 [inline]
> >  lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
> >  __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
> >  _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
> >  spin_lock include/linux/spinlock.h:349 [inline]
> >  padata_do_serial+0x21e/0x4b0 kernel/padata.c:392
> >  pcrypt_aead_enc+0x57/0x70 crypto/pcrypt.c:89
> >  padata_do_parallel+0x87b/0xa10 kernel/padata.c:217
> >  pcrypt_aead_encrypt+0x39f/0x4d0 crypto/pcrypt.c:117
> >  crypto_aead_encrypt+0xaa/0xf0 crypto/aead.c:94
> >  tipc_aead_encrypt net/tipc/crypto.c:821 [inline]
> >  tipc_crypto_xmit+0xf7a/0x2af0 net/tipc/crypto.c:1756
> >  tipc_bearer_xmit_skb+0x1ed/0x410 net/tipc/bearer.c:557
> >  tipc_disc_timeout+0x75e/0xcb0 net/tipc/discover.c:335
> >  call_timer_fn+0x1a0/0x6b0 kernel/time/timer.c:1474
> >  expire_timers kernel/time/timer.c:1519 [inline]
> >  __run_timers.part.0+0x674/0xa80 kernel/time/timer.c:1790
> >  __run_timers kernel/time/timer.c:1768 [inline]
> >  run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1803
> >  __do_softirq+0x1d3/0x9c6 kernel/softirq.c:571
> >  invoke_softirq kernel/softirq.c:445 [inline]
> >  __irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
> >  irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
> >  sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1106
> >  </IRQ>
> 
> The changelog doesn't explain the problem or why the proposed solution
> fixes it.
> 
> If I can read these splats right, it seems lockdep is complaining about
> how a task can take the reorder lock when softirqs are enabled
> (SOFTIRQ-ON-W) as in the tls_push_record() stack, but also when it's in
> softirq context (IN-SOFTIRQ-W), as in the tipc_disc_timeout() stack.  So
> it should be enough to disable softirq here.

...to avoid a deadlock.  Helpful to include the impact to the user too.

> 
> > Signed-off-by: Edward Adam Davis <eadavis@sina.com>
> > Reported-by: syzbot+bc05445bc14148d51915@syzkaller.appspotmail.com
> > ---
> >  kernel/padata.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/padata.c b/kernel/padata.c
> > index e5819bb8bd1d..38c7b17da796 100644
> > --- a/kernel/padata.c
> > +++ b/kernel/padata.c
> > @@ -388,14 +388,15 @@ void padata_do_serial(struct padata_priv *padata)
> >  	int hashed_cpu = padata_cpu_hash(pd, padata->seq_nr);
> >  	struct padata_list *reorder = per_cpu_ptr(pd->reorder_list, hashed_cpu);
> >  	struct padata_priv *cur;
> > +	unsigned long flags;
> >  
> > -	spin_lock(&reorder->lock);
> > +	spin_lock_irqsave(&reorder->lock, flags);
> >  	/* Sort in ascending order of sequence number. */
> >  	list_for_each_entry_reverse(cur, &reorder->list, list)
> >  		if (cur->seq_nr < padata->seq_nr)
> >  			break;
> >  	list_add(&padata->list, &cur->list);
> > -	spin_unlock(&reorder->lock);
> > +	spin_unlock_irqrestore(&reorder->lock, flags);
> >  
> >  	/*
> >  	 * Ensure the addition to the reorder list is ordered correctly
> > -- 
> > 2.37.2
> >