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>
1 parent 9b3c0a0
utsname_sysctl.c
/*
* Copyright (C) 2007
*
* Author: Eric Biederman <ebiederm@xmision.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation, version 2 of the
* License.
*/
#include <linux/module.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/version.h>
#include <linux/sysctl.h>
static void *get_uts(ctl_table *table, int write)
{
char *which = table->data;
struct uts_namespace *uts_ns;
uts_ns = current->nsproxy->uts_ns;
which = (which - (char *)&init_uts_ns) + (char *)uts_ns;
if (!write)
down_read(&uts_sem);
else
down_write(&uts_sem);
return which;
}
static void put_uts(ctl_table *table, int write, void *which)
{
if (!write)
up_read(&uts_sem);
else
up_write(&uts_sem);
}
#ifdef CONFIG_PROC_FS
/*
* Special case of dostring for the UTS structure. This has locks
* to observe. Should this be in kernel/sys.c ????
*/
static int proc_do_uts_string(ctl_table *table, int write, struct file *filp,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
struct ctl_table uts_table;
int r;
memcpy(&uts_table, table, sizeof(uts_table));
uts_table.data = get_uts(table, write);
r = proc_dostring(&uts_table,write,filp,buffer,lenp, ppos);
put_uts(table, write, uts_table.data);
return r;
}
#else
#define proc_do_uts_string NULL
#endif
#ifdef CONFIG_SYSCTL_SYSCALL
/* The generic string strategy routine: */
static int sysctl_uts_string(ctl_table *table, int __user *name, int nlen,
void __user *oldval, size_t __user *oldlenp,
void __user *newval, size_t newlen)
{
struct ctl_table uts_table;
int r, write;
write = newval && newlen;
memcpy(&uts_table, table, sizeof(uts_table));
uts_table.data = get_uts(table, write);
r = sysctl_string(&uts_table, name, nlen,
oldval, oldlenp, newval, newlen);
put_uts(table, write, uts_table.data);
return r;
}
#else
#define sysctl_uts_string NULL
#endif
static struct ctl_table uts_kern_table[] = {
{
.ctl_name = KERN_OSTYPE,
.procname = "ostype",
.data = init_uts_ns.name.sysname,
.maxlen = sizeof(init_uts_ns.name.sysname),
.mode = 0444,
.proc_handler = proc_do_uts_string,
.strategy = sysctl_uts_string,
},
{
.ctl_name = KERN_OSRELEASE,
.procname = "osrelease",
.data = init_uts_ns.name.release,
.maxlen = sizeof(init_uts_ns.name.release),
.mode = 0444,
.proc_handler = proc_do_uts_string,
.strategy = sysctl_uts_string,
},
{
.ctl_name = KERN_VERSION,
.procname = "version",
.data = init_uts_ns.name.version,
.maxlen = sizeof(init_uts_ns.name.version),
.mode = 0444,
.proc_handler = proc_do_uts_string,
.strategy = sysctl_uts_string,
},
{
.ctl_name = KERN_NODENAME,
.procname = "hostname",
.data = init_uts_ns.name.nodename,
.maxlen = sizeof(init_uts_ns.name.nodename),
.mode = 0644,
.proc_handler = proc_do_uts_string,
.strategy = sysctl_uts_string,
},
{
.ctl_name = KERN_DOMAINNAME,
.procname = "domainname",
.data = init_uts_ns.name.domainname,
.maxlen = sizeof(init_uts_ns.name.domainname),
.mode = 0644,
.proc_handler = proc_do_uts_string,
.strategy = sysctl_uts_string,
},
{}
};
static struct ctl_table uts_root_table[] = {
{
.ctl_name = CTL_KERN,
.procname = "kernel",
.mode = 0555,
.child = uts_kern_table,
},
{}
};
static int __init utsname_sysctl_init(void)
{
register_sysctl_table(uts_root_table);
return 0;
}
__initcall(utsname_sysctl_init);
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