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Btrfs: use rcu to protect device->name

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Al pointed out that we can just toss out the old name on a device and add a
new one arbitrarily, so anybody who uses device->name in printk could
possibly use free'd memory.  Instead of adding locking around all of this he
suggested doing it with RCU, so I've introduced a struct rcu_string that
does just that and have gone through and protected all accesses to
device->name that aren't under the uuid_mutex with rcu_read_lock().  This
protects us and I will use it for dealing with removing the device that we
used to mount the file system in a later patch.  Thanks,

Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <josef@redhat.com>
This commit is contained in:
Josef Bacik
2012-06-04 14:03:51 -04:00
committed by Chris Mason
parent 17ca04aff7
commit 606686eeac
8 changed files with 162 additions and 64 deletions
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56
fs/btrfs/rcu-string.h Normal file
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/*
* Copyright (C) 2012 Red Hat. All rights reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
struct rcu_string {
struct rcu_head rcu;
char str[0];
};
static inline struct rcu_string *rcu_string_strdup(const char *src, gfp_t mask)
{
size_t len = strlen(src) + 1;
struct rcu_string *ret = kzalloc(sizeof(struct rcu_string) +
(len * sizeof(char)), mask);
if (!ret)
return ret;
strncpy(ret->str, src, len);
return ret;
}
static inline void rcu_string_free(struct rcu_string *str)
{
if (str)
kfree_rcu(str, rcu);
}
#define printk_in_rcu(fmt, ...) do { \
rcu_read_lock(); \
printk(fmt, __VA_ARGS__); \
rcu_read_unlock(); \
} while (0)
#define printk_ratelimited_in_rcu(fmt, ...) do { \
rcu_read_lock(); \
printk_ratelimited(fmt, __VA_ARGS__); \
rcu_read_unlock(); \
} while (0)
#define rcu_str_deref(rcu_str) ({ \
struct rcu_string *__str = rcu_dereference(rcu_str); \
__str->str; \
})