[LU-16276] stale data read with simple IOR testing.

Wed, 14 Dec 2022 16:04:37 +0000

CLIO violates a Linux kernel MM protocol.
Linux kernel expect vmpage ref will released immedetely after
page->private clear. But CLIO broke it.
It caused race ll_releasepage vs bl ast handler,
ll_releasepage remove a page->private, but bl_ast handler take a
cl_page reference in same time.
It caused vmpage still in the mapping after __remove_mapping call,
because vmpage->_refcount isn't decresed.
So we needs to stay with kernel protocol and release a pageref after
cl_page_delete call.

lustre debug logs indicate it

00000008:00000001:9.0:1666910059.632700:0:5016:0:(osc_cache.c:3088:osc_page_gang_lookup()) Process entered

bl ast enter and interrrupted by ll_releasepage aka cache flush.
but cl_page ref was hold where

00000020:00000001:8.0:1666910059.632703:0:11668:0:(cl_page.c:545:cl_vmpage_page()) Process leaving (rc=18446624413482391544 : -119660227160072 : ffff932b6eaa97f8)
00000020:00000001:8.0:1666910059.632708:0:11668:0:(cl_page.c:444:cl_page_state_set0()) page@ffff932b6eaa97f8[3 ffff932b5cd3f2b0 1 1 0000000000000000]
00000020:00000001:8.0:1666910059.632709:0:11668:0:(cl_page.c:445:cl_page_state_set0()) page fffff2cc04e941c0 map ffff932c62810218 index 82632 flags 17ffffc0002015 count 3 priv ffff932b6eaa97f8:
00000020:00000001:8.0:1666910059.633545:0:11668:0:(cl_page.c:489:cl_pagevec_put()) page@ffff932b6eaa97f8[2 ffff932b5cd3f2b0 5 1 0000000000000000]
00000020:00000001:8.0:1666910059.633546:0:11668:0:(cl_page.c:490:cl_pagevec_put()) page fffff2cc04e941c0 map ffff932c62810218 index 82632 flags 17ffffc0000015 count 3 priv 0:
00000080:00008000:8.0:1666910059.633548:0:11668:0:(rw26.c:175:ll_releasepage()) page fffff2cc04e941c0 map ffff932c62810218 index 82632 flags 17ffffc0000015 count 3 priv 0: clpage ffff932b6eaa97f8 : 1
ll_releasepage exit and expect to free a cl_page but ref hold by BL AST thread.
and vmpage still with 3 refs while __remove_mapping whats 2. 
so __remove_mapping will fail with freeze refs.

00000020:00000001:9.0:1666910059.642999:0:5016:0:(cl_page.c:489:cl_pagevec_put()) page@ffff932b6eaa97f8[1 ffff932b5cd3f2b0 5 1 0000000000000000]
00000020:00000001:9.0:1666910059.643000:0:5016:0:(cl_page.c:490:cl_pagevec_put()) page fffff2cc04e941c0 map ffff932c62810218 index 82632 flags 17ffffc0000014 count 2 priv 0:
00000020:00000010:9.0:1666910059.643003:0:5016:0:(cl_page.c:178:__cl_page_free()) slab-freed 'cl_page': 472 at ffff932b6eaa97f8.

cl_page freed -> vmpage ref released, vmpage with 2refs and it may removed from pagecache, but none want's to do it and uptodate page still in pagecache.

bug introduced


fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  56) static void vvp_page_fini_common(struct ccc_page *cp)
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  57) {
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  58)         cfs_page_t *vmpage = cp->cpg_page;
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  59)
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  60)         LASSERT(vmpage != NULL);
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  61)         page_cache_release(vmpage);
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  62)         OBD_SLAB_FREE_PTR(cp, vvp_page_kmem);
fbf5870b984 (nikita         2008-11-07 23:54:43 +0000  63) }

Whamcloud Community JIRA

[LU-16276] stale data read with simple IOR testing.