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fault-inject: use prandom where cryptographically secure randomness is not needed

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Currently get_random*() is used to determine the probability of fault
injection, but cryptographically secure random numbers are not required.

There is no big problem in using prandom instead of get_random*() to
determine the probability of fault injection, and it also avoids acquiring
a spinlock, which is unsafe in some contexts.

[akpm@linux-foundation.org: tweak and reflow comment]
Link: https://lore.kernel.org/lkml/20241129120939.GG35539@noisy.programming.kicks-ass.net
Link: https://lkml.kernel.org/r/20241208142415.205960-1-akinobu.mita@gmail.com
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Akinobu Mita 2024-12-08 23:24:15 +09:00 committed by Andrew Morton
parent 3735c5225b
commit e9bc360b10
1 changed files with 26 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

28
lib/fault-inject.c
View file

@ -1,7 +1,7 @@
// SPDX-License-Identifier: GPL-2.0-only // SPDX-License-Identifier: GPL-2.0-only
#include <linux/kernel.h> #include <linux/kernel.h>
#include <linux/init.h> #include <linux/init.h>
#include <linux/random.h> #include <linux/prandom.h>
#include <linux/debugfs.h> #include <linux/debugfs.h>
#include <linux/sched.h> #include <linux/sched.h>
#include <linux/stat.h> #include <linux/stat.h>
@ -12,6 +12,24 @@
#include <linux/stacktrace.h> #include <linux/stacktrace.h>
#include <linux/fault-inject.h> #include <linux/fault-inject.h>
/*
* The should_fail() functions use prandom instead of the normal Linux RNG
* since they don't need cryptographically secure random numbers.
*/
static DEFINE_PER_CPU(struct rnd_state, fault_rnd_state);
static u32 fault_prandom_u32_below_100(void)
{
struct rnd_state *state;
u32 res;
state = &get_cpu_var(fault_rnd_state);
res = prandom_u32_state(state);
put_cpu_var(fault_rnd_state);
return res % 100;
}
/* /*
* setup_fault_attr() is a helper function for various __setup handlers, so it * setup_fault_attr() is a helper function for various __setup handlers, so it
* returns 0 on error, because that is what __setup handlers do. * returns 0 on error, because that is what __setup handlers do.
@ -31,6 +49,8 @@ int setup_fault_attr(struct fault_attr *attr, char *str)
return 0; return 0;
} }
prandom_init_once(&fault_rnd_state);
attr->probability = probability; attr->probability = probability;
attr->interval = interval; attr->interval = interval;
atomic_set(&attr->times, times); atomic_set(&attr->times, times);
@ -146,7 +166,7 @@ bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags)
return false; return false;
} }
if (attr->probability <= get_random_u32_below(100)) if (attr->probability <= fault_prandom_u32_below_100())
return false; return false;
fail: fail:
@ -219,6 +239,8 @@ struct dentry *fault_create_debugfs_attr(const char *name,
if (IS_ERR(dir)) if (IS_ERR(dir))
return dir; return dir;
prandom_init_once(&fault_rnd_state);
debugfs_create_ul("probability", mode, dir, &attr->probability); debugfs_create_ul("probability", mode, dir, &attr->probability);
debugfs_create_ul("interval", mode, dir, &attr->interval); debugfs_create_ul("interval", mode, dir, &attr->interval);
debugfs_create_atomic_t("times", mode, dir, &attr->times); debugfs_create_atomic_t("times", mode, dir, &attr->times);
@ -431,6 +453,8 @@ static const struct config_item_type fault_config_type = {
void fault_config_init(struct fault_config *config, const char *name) void fault_config_init(struct fault_config *config, const char *name)
{ {
prandom_init_once(&fault_rnd_state);
config_group_init_type_name(&config->group, name, &fault_config_type); config_group_init_type_name(&config->group, name, &fault_config_type);
} }
EXPORT_SYMBOL_GPL(fault_config_init); EXPORT_SYMBOL_GPL(fault_config_init);