Re: Hitting BUG_ON trap in read_pages() - : [PATCH v2] mm: Optimise put_pages_list()

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On Tue, Nov 09, 2021 at 07:45:47PM +0900, Namjae Jeon wrote:
> Hi Matthew,
> 
> This patch is hitting BUG_ON trap in read_pages() when running
> xfstests for cifs.
> There seems to be a same issue with other filesystems using .readpages ?

The real fix, of course, is to migrate away from using ->readpages ;-)
I think both 9p and nfs are going away this cycle.  CIFS really needs
to move to using the netfs interfaces.

> Could you please take a look ?

Please try this patch:

While free_unref_page_list() puts pages onto the CPU local LRU list, it
does not remove them from the list they were passed in on.  That makes
the list_head appear to be non-empty, and would lead to various corruption
problems if we didn't have an assertion that the list was empty.

Reinitialise the list after calling free_unref_page_list() to avoid
this problem.

Fixes: 988c69f1bc23 ("mm: optimise put_pages_list()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

diff --git a/mm/swap.c b/mm/swap.c
index 1841c24682f8..e8c9dc6d0377 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -156,6 +156,7 @@ void put_pages_list(struct list_head *pages)
 	}
 
 	free_unref_page_list(pages);
+	INIT_LIST_HEAD(pages);
 }
 EXPORT_SYMBOL(put_pages_list);
 



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