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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File | Mode | Size |
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Kconfig | -rw-r--r-- | 4.8 KB |
Makefile | -rw-r--r-- | 1.1 KB |
aes_ccm.c | -rw-r--r-- | 3.4 KB |
aes_ccm.h | -rw-r--r-- | 847 bytes |
cfg.c | -rw-r--r-- | 14.9 KB |
cfg.h | -rw-r--r-- | 155 bytes |
debugfs.c | -rw-r--r-- | 13.3 KB |
debugfs.h | -rw-r--r-- | 481 bytes |
debugfs_key.c | -rw-r--r-- | 7.0 KB |
debugfs_key.h | -rw-r--r-- | 1.2 KB |
debugfs_netdev.c | -rw-r--r-- | 10.6 KB |
debugfs_netdev.h | -rw-r--r-- | 944 bytes |
debugfs_sta.c | -rw-r--r-- | 7.6 KB |
debugfs_sta.h | -rw-r--r-- | 404 bytes |
event.c | -rw-r--r-- | 1.2 KB |
ieee80211.c | -rw-r--r-- | 37.7 KB |
ieee80211_i.h | -rw-r--r-- | 25.5 KB |
ieee80211_iface.c | -rw-r--r-- | 7.7 KB |
ieee80211_ioctl.c | -rw-r--r-- | 29.7 KB |
ieee80211_key.h | -rw-r--r-- | 3.1 KB |
ieee80211_led.c | -rw-r--r-- | 4.1 KB |
ieee80211_led.h | -rw-r--r-- | 1.3 KB |
ieee80211_rate.c | -rw-r--r-- | 5.7 KB |
ieee80211_rate.h | -rw-r--r-- | 5.4 KB |
ieee80211_sta.c | -rw-r--r-- | 100.4 KB |
key.c | -rw-r--r-- | 6.7 KB |
michael.c | -rw-r--r-- | 2.1 KB |
michael.h | -rw-r--r-- | 523 bytes |
rc80211_pid.h | -rw-r--r-- | 7.9 KB |
rc80211_pid_algo.c | -rw-r--r-- | 16.1 KB |
rc80211_pid_debugfs.c | -rw-r--r-- | 5.8 KB |
rc80211_simple.c | -rw-r--r-- | 10.1 KB |
regdomain.c | -rw-r--r-- | 4.6 KB |
rx.c | -rw-r--r-- | 57.3 KB |
sta_info.c | -rw-r--r-- | 10.6 KB |
sta_info.h | -rw-r--r-- | 6.4 KB |
tkip.c | -rw-r--r-- | 10.1 KB |
tkip.h | -rw-r--r-- | 1.1 KB |
tx.c | -rw-r--r-- | 53.0 KB |
util.c | -rw-r--r-- | 13.1 KB |
wep.c | -rw-r--r-- | 9.5 KB |
wep.h | -rw-r--r-- | 1.3 KB |
wme.c | -rw-r--r-- | 14.7 KB |
wme.h | -rw-r--r-- | 1.2 KB |
wpa.c | -rw-r--r-- | 15.2 KB |
wpa.h | -rw-r--r-- | 891 bytes |
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