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SubjectRe: [PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read()
On Tue, Feb 27, 2018 at 08:25:50AM +0800, Yang Shi wrote:
> 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>

Ehh, bloody tags.
I didn't suggest _killable() variants, they're quite ugly because API
multiplies. access_remote_vm() could be converted to down_read_killable().

> --- 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);

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