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Subject[PATCH v1 net 02/16] sysctl: Add proc_dobool_lockless().
Date
A sysctl variable is accessed concurrently, and there is always a chance of
data-race. So, all readers and writers need some basic protection to avoid
load/store-tearing.

This patch changes proc_dobool() to use READ_ONCE()/WRITE_ONCE() internally
to fix a data-race on the sysctl side. For now, proc_dobool() itself is
tolerant to a data-race, but we still need to add annotations on the other
subsystem's side.

In case we miss such fixes, this patch converts proc_dobool() to a wrapper
of proc_dobool_lockless(). When we fix a data-race in the other subsystem,
we can explicitly set it as a handler.

Also, this patch removes proc_dobool()'s document and adds
proc_dobool_lockless()'s one so that no one will use proc_dobool() anymore.

Fixes: a2071573d634 ("sysctl: introduce new proc handler proc_dobool")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
CC: Jia He <hejianet@gmail.com>
---
include/linux/sysctl.h | 2 ++
kernel/sysctl.c | 23 ++++++++++++++++-------
2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 9beab3a4de3d..fcafc16abbad 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -83,6 +83,8 @@ PROC_HANDLER(proc_dointvec_ms_jiffies);
PROC_HANDLER(proc_do_large_bitmap);
PROC_HANDLER(proc_do_static_key);

+PROC_HANDLER(proc_dobool_lockless);
+
/*
* Register a set of sysctl names by calling register_sysctl_table
* with an initialised array of struct ctl_table's. An entry with
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 1082c8bc5ba5..bc6fcc64eeaf 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -424,13 +424,12 @@ static void proc_put_char(void **buf, size_t *size, char c)
}

static int do_proc_dobool_conv(bool *negp, unsigned long *lvalp,
- int *valp,
- int write, void *data)
+ int *valp, int write, void *data)
{
if (write) {
- *(bool *)valp = *lvalp;
+ WRITE_ONCE(*(bool *)valp, *lvalp);
} else {
- int val = *(bool *)valp;
+ int val = READ_ONCE(*(bool *)valp);

*lvalp = (unsigned long)val;
*negp = false;
@@ -701,7 +700,7 @@ int do_proc_douintvec(struct ctl_table *table, int write,
}

/**
- * proc_dobool - read/write a bool
+ * proc_dobool_lockless - read/write a bool locklessly
* @table: the sysctl table
* @write: %TRUE if this is a write to the sysctl file
* @buffer: the user buffer
@@ -713,13 +712,19 @@ int do_proc_douintvec(struct ctl_table *table, int write,
*
* Returns 0 on success.
*/
-int proc_dobool(struct ctl_table *table, int write, void *buffer,
- size_t *lenp, loff_t *ppos)
+int proc_dobool_lockless(struct ctl_table *table, int write, void *buffer,
+ size_t *lenp, loff_t *ppos)
{
return do_proc_dointvec(table, write, buffer, lenp, ppos,
do_proc_dobool_conv, NULL);
}

+int proc_dobool(struct ctl_table *table, int write, void *buffer,
+ size_t *lenp, loff_t *ppos)
+{
+ return proc_dobool_lockless(table, write, buffer, lenp, ppos);
+}
+
/**
* proc_dointvec - read a vector of integers
* @table: the sysctl table
@@ -1497,6 +1502,8 @@ PROC_HANDLER_ENOSYS(proc_dointvec_ms_jiffies);
PROC_HANDLER_ENOSYS(proc_do_cad_pid);
PROC_HANDLER_ENOSYS(proc_do_large_bitmap);

+PROC_HANDLER_ENOSYS(proc_dobool_lockless);
+
#endif /* CONFIG_PROC_SYSCTL */

#if defined(CONFIG_SYSCTL)
@@ -2405,3 +2412,5 @@ EXPORT_SYMBOL(proc_dointvec_jiffies);
EXPORT_SYMBOL(proc_dointvec_userhz_jiffies);
EXPORT_SYMBOL(proc_dointvec_ms_jiffies);
EXPORT_SYMBOL(proc_do_large_bitmap);
+
+EXPORT_SYMBOL(proc_dobool_lockless);
--
2.30.2
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