linux-stable/fs/btrfs/rcu-string.h
Gustavo A. R. Silva 7593f4c53c btrfs: rcu-string: Replace zero-length array with flexible-array member
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member[1][2], introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning in
case the flexible array does not occur last in the structure, which will
help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by this
change:

 "Flexible array members have incomplete type, and so the sizeof operator
  may not be applied. As a quirk of the original implementation of
  zero-length arrays, sizeof evaluates to zero." [1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
2020-03-23 17:01:53 +01:00

48 lines
997 B
C

/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2012 Red Hat. All rights reserved.
*/
#ifndef BTRFS_RCU_STRING_H
#define BTRFS_RCU_STRING_H
struct rcu_string {
struct rcu_head rcu;
char str[];
};
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; \
})
#endif