[PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read()

[Yang Shi]

Like reading /proc/*/cmdline, it is possible to be blocked for long time
when reading /proc/*/environ when manipulating large mapping at the mean
time. The environ reading process will be waiting for mmap_sem become
available for a long time then it may cause the reading task hung.

Convert down_read() and access_remote_vm() to killable version.

Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Suggested-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---
 fs/proc/base.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9bdb84b..d87d9ab 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -933,7 +933,9 @@ static ssize_t environ_read(struct file *file, char __user *buf,
 	if (!mmget_not_zero(mm))
 		goto free;
 
-	down_read(&mm->mmap_sem);
+	ret = down_read_killable(&mm->mmap_sem);
+	if (ret)
+		goto out_mmput;
 	env_start = mm->env_start;
 	env_end = mm->env_end;
 	up_read(&mm->mmap_sem);
@@ -950,7 +952,8 @@ static ssize_t environ_read(struct file *file, char __user *buf,
 		max_len = min_t(size_t, PAGE_SIZE, count);
 		this_len = min(max_len, this_len);
 
-		retval = access_remote_vm(mm, (env_start + src), page, this_len, 0);
+		retval = access_remote_vm_killable(mm, (env_start + src),
+						page, this_len, 0);
 
 		if (retval <= 0) {
 			ret = retval;
@@ -968,6 +971,8 @@ static ssize_t environ_read(struct file *file, char __user *buf,
 		count -= retval;
 	}
 	*ppos = src;
+
+out_mmput:
 	mmput(mm);
 
 free:
-- 
1.8.3.1