Eric, sorry for delay.
On 05/29, Eric W. Biederman wrote:
>
> Oleg Nesterov <o...@redhat.com> writes:
>
> > Why the empty "." + ".." dir is bad if the task(s) has gone away after
> > opendir?
>
> Because the definition of a deleted directory that you are in is that
> getdents will return -ENOENT.
>
> You can reproduce this with any linux filesystem.
> mkdir foo
> cd foo
> rmdir ../foo
> strace -f ls .
>
> open(".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
> getdents(3, 0x1851c88, 32768) = -1 ENOENT (No such file or
> directory)
> close(3) = 0
Heh. Indeed, vfs_readdir() checks IS_DEADDIR().
Thanks.
OK. But this means that even 1/3 is not 100% right, exactly because
leader can be unhashed right before first_tid() takes rcu lock. Easy
to fix, we should simply factor out the "nr != 0" check.
And this also means that 3/3 is not right by the same reason. I'll
make a simpler patch which only avoids the unnecessary get/put in
proc_task_readdir().
Unless we can tolerate this very unlikely rase when the leader goes
away after initial ENOENT check at the start, of course... Or unless
we add canceldir() which resets getdents_callback->previous so that
we could return ENOENT after filldir() was already called ;)
Thanks Eric. I'll send v2.
Oleg.
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