linux-kernel - Re: [syzbot] [mm?] WARNING in copy

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Message-ID: <20250828114755.5981-1-hdanton@sina.com>
Date: Thu, 28 Aug 2025 19:47:54 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+69c74d38464686431506@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING in copy_process

> Date: Wed, 27 Aug 2025 16:15:31 -0700	[thread overview]
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    7fa4d8dc380f Add linux-next specific files for 20250821
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1036def0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ae76068823a236b3
> dashboard link: https://syzkaller.appspot.com/bug?extid=69c74d38464686431506
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13595c62580000

#syz test

--- x/mm/oom_kill.c
+++ y/mm/oom_kill.c
@@ -997,6 +997,8 @@ static void __oom_kill_process(struct ta
 		queue_oom_reaper(victim);
 
 	mmdrop(mm);
+	write_lock_irq(&tasklist_lock);
+	write_unlock_irq(&tasklist_lock);
 	put_task_struct(victim);
 }
 
@@ -1031,6 +1033,8 @@ static void oom_kill_process(struct oom_
 		mark_oom_victim(victim);
 		queue_oom_reaper(victim);
 		task_unlock(victim);
+		write_lock_irq(&tasklist_lock);
+		write_unlock_irq(&tasklist_lock);
 		put_task_struct(victim);
 		return;
 	}
--- x/mm/page-writeback.c
+++ y/mm/page-writeback.c
@@ -3014,7 +3014,7 @@ bool __folio_end_writeback(struct folio
 
 	if (mapping && mapping_use_writeback_tags(mapping)) {
 		struct inode *inode = mapping->host;
-		struct bdi_writeback *wb = inode_to_wb(inode);
+		struct bdi_writeback *wb;
 		unsigned long flags;
 
 		xa_lock_irqsave(&mapping->i_pages, flags);
@@ -3022,6 +3022,7 @@ bool __folio_end_writeback(struct folio
 		__xa_clear_mark(&mapping->i_pages, folio_index(folio),
 					PAGECACHE_TAG_WRITEBACK);
 
+		wb = inode_to_wb(inode);
 		wb_stat_mod(wb, WB_WRITEBACK, -nr);
 		__wb_writeout_add(wb, nr);
 		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
@@ -3054,7 +3055,7 @@ void __folio_start_writeback(struct foli
 	if (mapping && mapping_use_writeback_tags(mapping)) {
 		XA_STATE(xas, &mapping->i_pages, folio_index(folio));
 		struct inode *inode = mapping->host;
-		struct bdi_writeback *wb = inode_to_wb(inode);
+		struct bdi_writeback *wb;
 		unsigned long flags;
 		bool on_wblist;
 
@@ -3065,6 +3066,7 @@ void __folio_start_writeback(struct foli
 		on_wblist = mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK);
 
 		xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
+		wb = inode_to_wb(inode);
 		wb_stat_mod(wb, WB_WRITEBACK, nr);
 		if (!on_wblist) {
 			wb_inode_writeback_start(wb);
--