On Tue, Sep 15, 2020 at 11:27 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Every one of them is in the "io_schedule()" in the filemap_fault()
> path, although two of them seem to be in file_fdatawait_range() rather
> than in the lock_page() code itself (so they are also waiting on a
> page bit, but they are waiting for the writeback bit to clear).
No, that seems to be just stale entries on the stack from a previous
system call, rather than a real trace. There's no way to reach
file_fdatawait_range() from mlockall() that I can see.
So I'm not entirely sure why the stack trace for two of the processes
looks a bit different, but they all look like they should be in
__lock_page_killable().
It's possible those two were woken up (by another CPU) and their stack
is in flux. They also have "wake_up_page_bit()" as a stale entry on
their stack, so that's not entirely unlikely.
So that sysrq-W state shows that yes, people are stuck waiting for a
page, but that wasn't exactly unexpected.
Linus
