linux-ext4 - Re: [BUG RERPORT] BUG_ON(!list_empty(&inode->i_wb

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Date:   Thu, 6 May 2021 14:13:40 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     Al Viro <viro@...iv.linux.org.uk>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        <linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
        "zhangyi (F)" <yi.zhang@...wei.com>, Hou Tao <houtao1@...wei.com>,
        Ye Bin <yebin10@...wei.com>
Subject: Re: [BUG RERPORT] BUG_ON(!list_empty(&inode->i_wb_list))



在 2021/5/5 20:06, Jan Kara 写道:
> On Wed 05-05-21 17:07:33, yangerkun wrote:
>> Our syzkaller test trigger this BUG_ON in clear_inode:
>>
>> [   95.235069] Killed process 7637 (syz-executor) total-vm:37044kB,
>> anon-rss:76kB, file-rss:632kB, shmem-rss:0kB
>> [   95.238504] Memory cgroup out of memory: Kill process 284 (syz-executor)
>> score 187000 or sacrifice child
>> [   95.240419] Killed process 284 (syz-executor) total-vm:37044kB,
>> anon-rss:76kB, file-rss:632kB, shmem-rss:0kB
>> [   95.263244] Injecting memory failure for pfn 0x3a5876 at process virtual
>> address 0x20ffd000
>> [   95.282421] Memory failure: 0x3a5876: recovery action for dirty LRU page:
>> Recovered
>> [   95.283992] Injecting memory failure for pfn 0x3a6005 at process virtual
>> address 0x20ffe000
>> [   95.379135] Memory failure: 0x3a6005: recovery action for dirty LRU page:
>> Recovered
>> [   95.380853] Injecting memory failure for pfn 0x3a7048 at process virtual
>> address 0x20fff000
>> [   95.422596] Memory failure: 0x3a7048: recovery action for dirty LRU page:
>> Recovered
>> [   95.596571] JBD2: Detected IO errors while flushing file data on vda-8
>> [   95.858655] device bridge_slave_0 left promiscuous mode
>> [   95.870838] bridge0: port 1(bridge_slave_0) entered disabled state
>> [   96.039754] ------------[ cut here ]------------
>> [   96.041176] kernel BUG at fs/inode.c:519!
> 
> So this is BUG_ON(!list_empty(&inode->i_wb_list)) I assume?

Yes.

> 
>> [   96.042424] Internal error: Oops - BUG: 0 [#1] SMP
>> [   96.043892] Dumping ftrace buffer:
>> [   96.044956]    (ftrace buffer empty)
>> [   96.046068] Modules linked in:
>> [   96.047104] Process syz-executor (pid: 7811, stack limit =
>> 0x000000009f3892d3)
>> [   96.049217] CPU: 1 PID: 7811 Comm: syz-executor Not tainted 4.19.95 #9
>> [   96.051144] Hardware name: linux,dummy-virt (DT)
>> [   96.052570] pstate: 80000005 (Nzcv daif -PAN -UAO)
>> [   96.054065] pc : clear_inode+0x280/0x2a8
>> [   96.055317] lr : clear_inode+0x280/0x2a8
>> [   96.056548] sp : ffff800352797950
>> [   96.057604] x29: ffff800352797950 x28: 0000000000000000
>> [   96.059295] x27: ffff800358854c00 x26: ffff800358854b70
>> [   96.060982] x25: ffff80036af01100 x24: ffff800369e48aa8
>> [   96.062673] x23: ffff80036af02600 x22: 0000000000047f3d
>> [   96.064358] x21: 0000000000000000 x20: ffff800358854c98
>> [   96.066025] x19: ffff800358854b70 x18: 0000000000000000
>> [   96.067703] x17: 0000000000000000 x16: 0000000000000000
>> [   96.069370] x15: 0000000000000000 x14: 0000000000000000
>> [   96.071049] x13: 0000000000000000 x12: 0000000000000000
>> [   96.072738] x11: 1ffff0006cfc1faf x10: 0000000000000ba0
>> [   96.074418] x9 : ffff8003527976a0 x8 : ffff800359511c00
>> [   96.076102] x7 : 1ffff0006cfc1f50 x6 : dfff200000000000
>> [   96.077783] x5 : 00000000f2f2f200 x4 : ffff800358854c98
>> [   96.079469] x3 : ffff200008000000 x2 : ffff200009867000
>> [   96.081145] x1 : ffff800359511000 x0 : 0000000000000000
>> [   96.082835] Call trace:
>> [   96.083725]  clear_inode+0x280/0x2a8
>> [   96.084886]  ext4_clear_inode+0x38/0xe8
>> [   96.086113]  ext4_free_inode+0x130/0xc68
>> [   96.087371]  ext4_evict_inode+0xb20/0xcb8
>> [   96.088648]  evict+0x1a8/0x3c0
>> [   96.089655]  iput+0x344/0x460
>> [   96.090639]  do_unlinkat+0x260/0x410
>> [   96.091802]  __arm64_sys_unlinkat+0x6c/0xc0
>> [   96.093143]  el0_svc_common+0xdc/0x3b0
>> [   96.094349]  el0_svc_handler+0xf8/0x160
>> [   96.095583]  el0_svc+0x10/0x218
>> [   96.096609] Code: 9413f4a9 d503201f f90017b6 97f4d5b1 (d4210000)
>> [   96.098542] ---[ end trace 93e81128c9262960 ]---
>>
>> The vmcore show that's a ext4 inode with order journal mode. The "Injecting
>> memory failure" will call me_pagecache_dirty and then trigger the "JBD2:
>> Detected IO" since it inject the EIO for this page.
>>
>> We have a guess show as latter(just guess...). memory_failure will decrease
>> nrpages to 0, then ext4_evict_inode won't use mapping->i_pages, so
>> list_del_init that end_page_writeback has did won't been seen since there is
>> no barrier can ensure that, and then trigger the BUG_ON.
>>
>> We have add some debug info the check this guess. But since it really hard
>> to trigger this again. So, does there anyone can help to recheck the guess,
>> or can help to give advise for this problem?
> 
> Hmm, I don't think what you propose can happen since clear_inode() cycles
> through i_pages lock and by the time clear_inode() is called,

You are right. Sorry for the mistake. I will try to increase the 
recurrence probability.

> end_page_writeback() must be holding this lock in order to clear
> PageWriteback bit. So there must be something else going on but so far I
> have no idea what it could be.
> 
> 								Honz >
>> end_page_writeback
>>    test_clear_page_writeback
>>      xa_lock_irqsave(&mapping->i_pages, flags)
>> 	TestClearPageWriteback(page)
>> 	sb_clear_inode_writeback
>> 	  list_del_init(&inode->i_wb_list)
>> 	xa_unlock_irqrestore(&mapping->i_pages, flags)
>>
>> memory_failure
>>    lock_page(p)
>>    wait_on_page_writeback(p)
>>    identify_page_state
>>      page_action
>> 	  me_pagecache_dirty
>> 	  mapping_set_error(mapping, -EIO)
>> 	  me_pagecache_clean(p, pfn)
>> 	    generic_error_remove_page
>> 		  truncate_inode_page(mapping, page)
>> 		    delete_from_page_cache
>> 			  xa_lock_irqsave(&mapping->i_pages, flags)
>> 			  __delete_from_page_cache(page, NULL)
>> 			    page_cache_tree_delete
>> 				  mapping->nrpages -= nr --> will decrease nrpages to 0
>> 			  xa_unlock_irqrestore(&mapping->i_pages, flags)
>>
>>
>> ext4_evict_inode
>>    truncate_inode_pages_final
>>      truncate_inode_pages
>> 	  truncate_inode_pages_range
>> 	     if (mapping->nrpages == 0 && mapping->nrexceptional == 0)
>> 		   goto out; --> won't lock mapping->i_pages, so no barrier can ensure we
>> see list_del_init