From: Matthew Wilcox <willy@infradead.org>
To: linux-mm@kvack.org
Subject: Rare memory leakage
Date: Tue, 22 Sep 2020 04:12:15 +0100 [thread overview]
Message-ID: <20200922031215.GZ32101@casper.infradead.org> (raw)
This is a fun little race.
Dramatis personae: Pages P0, P1 are consecutive and aligned.
Threads A, B, C.
Page P0 is allocated to the page cache.
Page P1 is free.
Thread A calls find_get_entry()
P0 is returned from xas_load()
Thread B removes the page from the page cache (eg truncate, invalidatepage).
P0 is buddy-merged with P1.
Thread C calls alloc_pages, order 1, does not specify GFP_COMP. P0 now
has refcount 1.
Thread A calls page_cache_get_speculative(). P0 has refcount 2.
Thread C calls __free_page(P0, 1)
put_page_testzero is _false_. Do not call free_the_page().
Thread A calls put_page(P0)
We free P0 and nobody knows to free P1.
Weird solution: In __free_page(), if put_page_testzero() fails and page
is not PageHead, convert it to a compound page. Then the put_page()
by Thread A will free P1.
Better ideas?
next reply other threads:[~2020-09-22 3:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 3:12 Matthew Wilcox [this message]
2020-09-22 3:43 ` Rare memory leakage Ira Weiny
2020-09-22 11:04 ` Matthew Wilcox
2020-09-22 11:22 ` Vlastimil Babka
2020-09-22 11:44 ` Matthew Wilcox
2020-09-22 13:12 ` Matthew Wilcox
2020-09-23 6:46 ` Kirill A. Shutemov
2020-09-23 11:26 ` Matthew Wilcox
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