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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802 | ||
8021q | ||
9p | ||
appletalk | ||
atm | ||
ax25 | ||
bluetooth | ||
bridge | ||
can | ||
core | ||
dccp | ||
decnet | ||
econet | ||
ethernet | ||
ieee80211 | ||
ipv4 | ||
ipv6 | ||
ipx | ||
irda | ||
iucv | ||
key | ||
lapb | ||
llc | ||
mac80211 | ||
netfilter | ||
netlabel | ||
netlink | ||
netrom | ||
packet | ||
rfkill | ||
rose | ||
rxrpc | ||
sched | ||
sctp | ||
sunrpc | ||
tipc | ||
unix | ||
wanrouter | ||
wireless | ||
x25 | ||
xfrm | ||
Kconfig | -rw-r--r-- | 8.5 KB |
Makefile | -rw-r--r-- | 1.6 KB |
TUNABLE | -rw-r--r-- | 2.2 KB |
compat.c | -rw-r--r-- | 16.6 KB |
nonet.c | -rw-r--r-- | 528 bytes |
socket.c | -rw-r--r-- | 55.1 KB |
sysctl_net.c | -rw-r--r-- | 1.8 KB |
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