[PATCH] mm: use mm.arg_lock in get_cmdline()

[Laurent Dufour]

The commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end
and env_start|end in mm_struct") introduce the spinlock arg_lock to protect
the arg_* and env_* field of the mm_struct structure.

While reading the code, I found that this new spinlock was not used in
get_cmdline() to protect access to these fields.

Fixing this even if there is no issue reported yet for this.

Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and 
env_start|end in mm_struct")
Cc: Yang Shi <yang....@linux.alibaba.com>
Signed-off-by: Laurent Dufour <lduf...@linux.ibm.com>
---
 mm/util.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 05a464929b3e..789760c3028b 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, 
int buflen)
        if (!mm->arg_end)
                goto out_mm;    /* Shh! No looking before we're done */
 
-       down_read(&mm->mmap_sem);
+       spin_lock(&mm->arg_lock);
        arg_start = mm->arg_start;
        arg_end = mm->arg_end;
        env_start = mm->env_start;
        env_end = mm->env_end;
-       up_read(&mm->mmap_sem);
+       spin_unlock(&mm->arg_lock);
 
        len = arg_end - arg_start;
 
-- 
2.21.0