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Subject[PATCH v1 net 07/16] sysctl: Add proc_doulongvec_minmax_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_doulongvec_minmax() to use READ_ONCE()/WRITE_ONCE()
internally to fix a data-race on the sysctl side. For now,
proc_doulongvec_minmax() 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_doulongvec_minmax() to
a wrapper of proc_doulongvec_minmax_lockless(). When we fix a data-race in
the other subsystem, we can explicitly set it as a handler.

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
include/linux/sysctl.h | 1 +
kernel/sysctl.c | 21 +++++++++++++++++----
2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 830d1a8f21d4..c23b6beef748 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -88,6 +88,7 @@ PROC_HANDLER(proc_dointvec_lockless);
PROC_HANDLER(proc_douintvec_lockless);
PROC_HANDLER(proc_dointvec_minmax_lockless);
PROC_HANDLER(proc_douintvec_minmax_lockless);
+PROC_HANDLER(proc_doulongvec_minmax_lockless);

/*
* Register a set of sysctl names by calling register_sysctl_table
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8ff57b8d1212..931ab58985f2 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1127,9 +1127,11 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table,
err = -EINVAL;
break;
}
- *i = val;
+
+ WRITE_ONCE(*i, val);
} else {
- val = convdiv * (*i) / convmul;
+ val = convdiv * READ_ONCE(*i) / convmul;
+
if (!first)
proc_put_char(&buffer, &left, '\t');
proc_put_long(&buffer, &left, val, false);
@@ -1157,7 +1159,8 @@ static int do_proc_doulongvec_minmax(struct ctl_table *table, int write,
}

/**
- * proc_doulongvec_minmax - read a vector of long integers with min/max values
+ * proc_doulongvec_minmax_lockless - read/write a vector of long integers
+ * with min/max values locklessly
* @table: the sysctl table
* @write: %TRUE if this is a write to the sysctl file
* @buffer: the user buffer
@@ -1172,10 +1175,18 @@ static int do_proc_doulongvec_minmax(struct ctl_table *table, int write,
*
* Returns 0 on success.
*/
+int proc_doulongvec_minmax_lockless(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ return do_proc_doulongvec_minmax(table, write, buffer, lenp, ppos,
+ 1l, 1l);
+}
+
int proc_doulongvec_minmax(struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
- return do_proc_doulongvec_minmax(table, write, buffer, lenp, ppos, 1l, 1l);
+ return proc_doulongvec_minmax_lockless(table, write, buffer,
+ lenp, ppos);
}

/**
@@ -1540,6 +1551,7 @@ PROC_HANDLER_ENOSYS(proc_dointvec_lockless);
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);

#endif /* CONFIG_PROC_SYSCTL */

@@ -2455,3 +2467,4 @@ EXPORT_SYMBOL(proc_dointvec_lockless);
EXPORT_SYMBOL(proc_douintvec_lockless);
EXPORT_SYMBOL(proc_dointvec_minmax_lockless);
EXPORT_SYMBOL_GPL(proc_douintvec_minmax_lockless);
+EXPORT_SYMBOL(proc_doulongvec_minmax_lockless);
--
2.30.2
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