Revision fb59e9f1e9786635ea12e12bf6adbb132e10f979 authored by Hugh Dickins on 04 March 2008, 22:29:16 UTC, committed by Linus Torvalds on 05 March 2008, 00:35:15 UTC
While testing force_empty, during an exit_mmap, __mem_cgroup_remove_list called from mem_cgroup_uncharge_page oopsed on a NULL pointer in the lru list. I couldn't see what racing tasks on other cpus were doing, but surmise that another must have been in mem_cgroup_charge_common on the same page, between its unlock_page_cgroup and spin_lock_irqsave near done (thanks to that kzalloc which I'd almost changed to a kmalloc). Normally such a race cannot happen, the ref_cnt prevents it, the final uncharge cannot race with the initial charge. But force_empty buggers the ref_cnt, that's what it's all about; and thereafter forced pages are vulnerable to races such as this (just think of a shared page also mapped into an mm of another mem_cgroup than that just emptied). And remain vulnerable until they're freed indefinitely later. This patch just fixes the oops by moving the unlock_page_cgroups down below adding to and removing from the list (only possible given the previous patch); and while we're at it, we might as well make it an invariant that page->page_cgroup is always set while pc is on lru. But this behaviour of force_empty seems highly unsatisfactory to me: why have a ref_cnt if we always have to cope with it being violated (as in the earlier page migration patch). We may prefer force_empty to move pages to an orphan mem_cgroup (could be the root, but better not), from which other cgroups could recover them; we might need to reverse the locking again; but no time now for such concerns. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Kconfig | -rw-r--r-- | 15.7 KB |
Makefile | -rw-r--r-- | 1.6 KB |
act_api.c | -rw-r--r-- | 23.0 KB |
act_gact.c | -rw-r--r-- | 5.4 KB |
act_ipt.c | -rw-r--r-- | 7.3 KB |
act_mirred.c | -rw-r--r-- | 6.1 KB |
act_nat.c | -rw-r--r-- | 7.1 KB |
act_pedit.c | -rw-r--r-- | 6.0 KB |
act_police.c | -rw-r--r-- | 9.1 KB |
act_simple.c | -rw-r--r-- | 5.1 KB |
cls_api.c | -rw-r--r-- | 13.3 KB |
cls_basic.c | -rw-r--r-- | 6.4 KB |
cls_flow.c | -rw-r--r-- | 14.4 KB |
cls_fw.c | -rw-r--r-- | 8.3 KB |
cls_route.c | -rw-r--r-- | 12.2 KB |
cls_rsvp.c | -rw-r--r-- | 761 bytes |
cls_rsvp.h | -rw-r--r-- | 14.6 KB |
cls_rsvp6.c | -rw-r--r-- | 768 bytes |
cls_tcindex.c | -rw-r--r-- | 11.8 KB |
cls_u32.c | -rw-r--r-- | 16.3 KB |
em_cmp.c | -rw-r--r-- | 2.1 KB |
em_meta.c | -rw-r--r-- | 21.2 KB |
em_nbyte.c | -rw-r--r-- | 1.9 KB |
em_text.c | -rw-r--r-- | 3.6 KB |
em_u32.c | -rw-r--r-- | 1.4 KB |
ematch.c | -rw-r--r-- | 14.6 KB |
sch_api.c | -rw-r--r-- | 29.9 KB |
sch_atm.c | -rw-r--r-- | 19.5 KB |
sch_blackhole.c | -rw-r--r-- | 1.2 KB |
sch_cbq.c | -rw-r--r-- | 47.1 KB |
sch_dsmark.c | -rw-r--r-- | 11.3 KB |
sch_fifo.c | -rw-r--r-- | 2.5 KB |
sch_generic.c | -rw-r--r-- | 14.8 KB |
sch_gred.c | -rw-r--r-- | 13.8 KB |
sch_hfsc.c | -rw-r--r-- | 40.4 KB |
sch_htb.c | -rw-r--r-- | 42.5 KB |
sch_ingress.c | -rw-r--r-- | 3.5 KB |
sch_netem.c | -rw-r--r-- | 17.3 KB |
sch_prio.c | -rw-r--r-- | 11.6 KB |
sch_red.c | -rw-r--r-- | 9.0 KB |
sch_sfq.c | -rw-r--r-- | 14.6 KB |
sch_tbf.c | -rw-r--r-- | 11.7 KB |
sch_teql.c | -rw-r--r-- | 11.4 KB |
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