[PATCH v1 net 08/16] sysctl: Add proc_dointvec_jiffies_lockless().

From: Kuniyuki Iwashima
Date: Wed Jul 06 2022 - 01:23:59 EST


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_dointvec_jiffies() to use READ_ONCE()/WRITE_ONCE()
internally to fix a data-race on the sysctl side. For now,
proc_dointvec_jiffies() 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_dointvec_jiffies() to
a wrapper of proc_dointvec_jiffies_lockless(). When we fix a data-race in
the other subsystem, we can explicitly set it as a handler.

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
---
include/linux/sysctl.h | 1 +
kernel/sysctl.c | 26 ++++++++++++++++++++------
2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index c23b6beef748..8747dbc721f5 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -89,6 +89,7 @@ PROC_HANDLER(proc_douintvec_lockless);
PROC_HANDLER(proc_dointvec_minmax_lockless);
PROC_HANDLER(proc_douintvec_minmax_lockless);
PROC_HANDLER(proc_doulongvec_minmax_lockless);
+PROC_HANDLER(proc_dointvec_jiffies_lockless);

/*
* Register a set of sysctl names by calling register_sysctl_table
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 931ab58985f2..11a1ce837623 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1221,10 +1221,15 @@ static int do_proc_dointvec_jiffies_conv(bool *negp, unsigned long *lvalp,
if (write) {
if (*lvalp > INT_MAX / HZ)
return 1;
- *valp = *negp ? -(*lvalp*HZ) : (*lvalp*HZ);
+
+ if (*negp)
+ WRITE_ONCE(*valp, -(*lvalp * HZ));
+ else
+ WRITE_ONCE(*valp, *lvalp * HZ);
} else {
- int val = *valp;
+ int val = READ_ONCE(*valp);
unsigned long lval;
+
if (val < 0) {
*negp = true;
lval = -(unsigned long)val;
@@ -1286,7 +1291,8 @@ static int do_proc_dointvec_ms_jiffies_conv(bool *negp, unsigned long *lvalp,
}

/**
- * proc_dointvec_jiffies - read a vector of integers as seconds
+ * proc_dointvec_jiffies_lockless - read/write a vector of integers as
+ * seconds locklessly
* @table: the sysctl table
* @write: %TRUE if this is a write to the sysctl file
* @buffer: the user buffer
@@ -1294,17 +1300,23 @@ static int do_proc_dointvec_ms_jiffies_conv(bool *negp, unsigned long *lvalp,
* @ppos: file position
*
* Reads/writes up to table->maxlen/sizeof(unsigned int) integer
- * values from/to the user buffer, treated as an ASCII string.
+ * values from/to the user buffer, treated as an ASCII string.
* The values read are assumed to be in seconds, and are converted into
* jiffies.
*
* Returns 0 on success.
*/
+int proc_dointvec_jiffies_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_dointvec_jiffies_conv, NULL);
+}
+
int proc_dointvec_jiffies(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_dointvec_jiffies_conv,NULL);
+ return proc_dointvec_jiffies_lockless(table, write, buffer, lenp, ppos);
}

/**
@@ -1552,6 +1564,7 @@ PROC_HANDLER_ENOSYS(proc_douintvec_lockless);
PROC_HANDLER_ENOSYS(proc_dointvec_minmax_lockless);
PROC_HANDLER_ENOSYS(proc_douintvec_minmax_lockless);
PROC_HANDLER_ENOSYS(proc_doulongvec_minmax_lockless);
+PROC_HANDLER_ENOSYS(proc_dointvec_jiffies_lockless);

#endif /* CONFIG_PROC_SYSCTL */

@@ -2468,3 +2481,4 @@ EXPORT_SYMBOL(proc_douintvec_lockless);
EXPORT_SYMBOL(proc_dointvec_minmax_lockless);
EXPORT_SYMBOL_GPL(proc_douintvec_minmax_lockless);
EXPORT_SYMBOL(proc_doulongvec_minmax_lockless);
+EXPORT_SYMBOL(proc_dointvec_jiffies_lockless);
--
2.30.2