kernel/tools/testing/radix-tree/iteration_check_2.c, branch linux-6.2.yHosts the 0x221E linux distro kernel.https://universe.0xinfinity.dev/distro/kernel/atom?h=linux-6.2.y2020-03-12T21:42:08Zxarray: Fix early termination of xas_for_each_marked2020-03-12T21:42:08ZMatthew Wilcox (Oracle)willy@infradead.org2020-03-12T21:29:11Zurn:sha1:7e934cf5ace1dceeb804f7493fa28bb697ed3c52
xas_for_each_marked() is using entry == NULL as a termination condition
of the iteration. When xas_for_each_marked() is used protected only by
RCU, this can however race with xas_store(xas, NULL) in the following
way:
TASK1 TASK2
page_cache_delete() find_get_pages_range_tag()
xas_for_each_marked()
xas_find_marked()
off = xas_find_chunk()
xas_store(&xas, NULL)
xas_init_marks(&xas);
...
rcu_assign_pointer(*slot, NULL);
entry = xa_entry(off);
And thus xas_for_each_marked() terminates prematurely possibly leading
to missed entries in the iteration (translating to missing writeback of
some pages or a similar problem).
If we find a NULL entry that has been marked, skip it (unless we're trying
to allocate an entry).
Reported-by: Jan Kara <jack@suse.cz>
CC: stable@vger.kernel.org
Fixes: ef8e5717db01 ("page cache: Convert delete_batch to XArray")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>