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....@linux.alibaba.com> > Suggested-by: Alexey Dobriyan <adobri...@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);
