linux-ext4 - Re: kernel/rcu/tree.c:1031 rcu_irq_enter() invoked with irqs enabled!!!!

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Date:   Tue, 25 Apr 2017 13:28:41 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Theodore Ts'o" <tytso@....edu>, linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: kernel/rcu/tree.c:1031 rcu_irq_enter() invoked with irqs
 enabled!!!!

On Tue, Apr 25, 2017 at 02:13:45PM -0600, Ross Zwisler wrote:
> I hit this RCU warning while running mkfs.ext4 on a PMEM namespace with
> an unmodified v4.11-rc8 (passed through kasan_symbolize.py):
> 
> ===============================
> [ ERR: suspicious RCU usage.  ]
> 4.11.0-rc8 #1 Not tainted
> -------------------------------
> kernel/rcu/tree.c:1031 rcu_irq_enter() invoked with irqs enabled!!!!

Just in case there is any doubt, invoking rcu_irq_enter() with irqs
enabled voids your kernel's RCU warranty.  ;-)

So please don't do that.

							Thanx, Paul

> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 0
> no locks held by mkfs.ext4/18493.
> 
> stack backtrace:
> CPU: 10 PID: 18493 Comm: mkfs.ext4 Not tainted 4.11.0-rc8 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc25 04/01/2014
> Call Trace:
> [<     inline     >] __dump_stack project/linux/lib/dump_stack.c:16
> [<      none      >] dump_stack+0x86/0xc3 project/linux/lib/dump_stack.c:52
> [<      none      >] lockdep_rcu_suspicious+0xd7/0x110 project/linux/kernel/locking/lockdep.c:4461
> [<      none      >] rcu_irq_enter+0x74/0x80 project/linux/kernel/rcu/tree.c:1031
> [<      none      >] kvm_async_pf_task_wait+0x1af/0x240 project/linux/arch/x86/kernel/kvm.c:164
> [<      none      >] do_async_page_fault+0x63/0x90 project/linux/arch/x86/kernel/kvm.c:269
>  ?[<      none      >] do_async_page_fault+0x63/0x90 project/linux/arch/x86/kernel/kvm.c:269
> [<      none      >] async_page_fault+0x28/0x30 project/linux_2/arch/x86/entry/entry_64.S:1014
> RIP: 0010:copy_user_enhanced_fast_string+0x5/0x10
> RSP: 0018:ffffc90008777c90 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 0000000000001000 RCX: 0000000000001000
> RDX: 0000000000001000 RSI: 00007f42a5d88010 RDI: ffff88007e82d000
> RBP: ffffc90008777ce0 R08: ffff88007e82d000 R09: 0000000000000000
> R10: 0000000000000000 R11: ffffea0001fa0b40 R12: 0000000000001000
> R13: ffffc90008777e50 R14: ffff88007e82e000 R15: 0000000000001000
>  ?[<     inline     >] copy_user_generic project/linux/./arch/x86/include/asm/uaccess_64.h:37
>  ?[<     inline     >] __copy_from_user_nocheck project/linux/./arch/x86/include/asm/uaccess_64.h:59
>  ?[<     inline     >] __copy_from_user_inatomic project/linux/./arch/x86/include/asm/uaccess_64.h:251
>  ?[<      none      >] iov_iter_copy_from_user_atomic+0xbb/0x350 project/linux/lib/iov_iter.c:721
> [<      none      >] generic_perform_write+0xf2/0x1d0 project/linux/mm/filemap.c:2843
> [<      none      >] __generic_file_write_iter+0x185/0x1c0 project/linux/mm/filemap.c:2960
> [<      none      >] blkdev_write_iter+0x96/0x110 project/linux/fs/block_dev.c:2008
> [<     inline     >] call_write_iter project/linux/./include/linux/fs.h:1733
> [<     inline     >] new_sync_write project/linux/fs/read_write.c:497
> [<      none      >] __vfs_write+0xe8/0x160 project/linux/fs/read_write.c:510
>  ?[<     inline     >] call_write_iter project/linux/./include/linux/fs.h:1733
>  ?[<     inline     >] new_sync_write project/linux/fs/read_write.c:497
>  ?[<      none      >] __vfs_write+0xe8/0x160 project/linux/fs/read_write.c:510
> [<      none      >] vfs_write+0xcb/0x1f0 project/linux/fs/read_write.c:558
> [<     inline     >] SYSC_pwrite64 project/linux/fs/read_write.c:647
> [<      none      >] SyS_pwrite64+0x98/0xc0 project/linux/fs/read_write.c:634
> [<      none      >] entry_SYSCALL_64_fastpath+0x1f/0xc2 project/linux_2/arch/x86/entry/entry_64.S:204
> RIP: 0033:0x7f42acd4d213
> RSP: 002b:00007ffc846e4e38 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f42acd4d213
> RDX: 00000000001e0000 RSI: 00007f42a5c9f010 RDI: 0000000000000003
> RBP: 0000559bd6c46380 R08: 00007f42a5c9f010 R09: 0000000000000200
> R10: 0000000680820000 R11: 0000000000000246 R12: 00007ffc846e4f9c
> R13: 0000000000000425 R14: 0000000000000200 R15: 0000559bd6c46380
>