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| author | Sultan Alsawaf <sultan@kerneltoast.com> | 2022-05-13 15:11:26 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-06-06 08:24:21 +0200 |
| commit | 645996efc2ae391246d595832aaa6f9d3cc338c7 (patch) | |
| tree | 93a8c8622b8bc20acd6f8eb3380983cbd0985faf | |
| parent | 92a999d1963eed0df666284e20055136ceabd12f (diff) | |
| download | omap-645996efc2ae391246d595832aaa6f9d3cc338c7.tar.gz | |
zsmalloc: fix races between asynchronous zspage free and page migration
commit 2505a981114dcb715f8977b8433f7540854851d8 upstream.
The asynchronous zspage free worker tries to lock a zspage's entire page
list without defending against page migration. Since pages which haven't
yet been locked can concurrently migrate off the zspage page list while
lock_zspage() churns away, lock_zspage() can suffer from a few different
lethal races.
It can lock a page which no longer belongs to the zspage and unsafely
dereference page_private(), it can unsafely dereference a torn pointer to
the next page (since there's a data race), and it can observe a spurious
NULL pointer to the next page and thus not lock all of the zspage's pages
(since a single page migration will reconstruct the entire page list, and
create_page_chain() unconditionally zeroes out each list pointer in the
process).
Fix the races by using migrate_read_lock() in lock_zspage() to synchronize
with page migration.
Link: https://lkml.kernel.org/r/20220509024703.243847-1-sultan@kerneltoast.com
Fixes: 77ff465799c602 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | mm/zsmalloc.c | 37 |
1 files changed, 33 insertions, 4 deletions
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 11e81b3ff0cf..4d71356ea66a 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1812,11 +1812,40 @@ static enum fullness_group putback_zspage(struct size_class *class, */ static void lock_zspage(struct zspage *zspage) { - struct page *page = get_first_page(zspage); + struct page *curr_page, *page; - do { - lock_page(page); - } while ((page = get_next_page(page)) != NULL); + /* + * Pages we haven't locked yet can be migrated off the list while we're + * trying to lock them, so we need to be careful and only attempt to + * lock each page under migrate_read_lock(). Otherwise, the page we lock + * may no longer belong to the zspage. This means that we may wait for + * the wrong page to unlock, so we must take a reference to the page + * prior to waiting for it to unlock outside migrate_read_lock(). + */ + while (1) { + migrate_read_lock(zspage); + page = get_first_page(zspage); + if (trylock_page(page)) + break; + get_page(page); + migrate_read_unlock(zspage); + wait_on_page_locked(page); + put_page(page); + } + + curr_page = page; + while ((page = get_next_page(curr_page))) { + if (trylock_page(page)) { + curr_page = page; + } else { + get_page(page); + migrate_read_unlock(zspage); + wait_on_page_locked(page); + put_page(page); + migrate_read_lock(zspage); + } + } + migrate_read_unlock(zspage); } static struct dentry *zs_mount(struct file_system_type *fs_type, |