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Date:   Wed, 5 May 2021 17:07:33 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     Al Viro <viro@...iv.linux.org.uk>,
        "Theodore Y . Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        <linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>
CC:     <yangerkun@...wei.com>, "zhangyi (F)" <yi.zhang@...wei.com>,
        Hou Tao <houtao1@...wei.com>, Ye Bin <yebin10@...wei.com>
Subject: [BUG RERPORT] BUG_ON(!list_empty(&inode->i_wb_list))

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!
[   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?


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

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