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Subject[PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read()
Date
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@linux.alibaba.com>
Suggested-by: Alexey Dobriyan <adobriyan@gmail.com>
---
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
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