[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <0ab6524a-6917-efe2-de69-f07fb5cdd9d2@redhat.com>
Date: Wed, 9 Aug 2023 20:04:04 +0200
From: David Hildenbrand <david@...hat.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, willy@...radead.org, hannes@...xchg.org,
mhocko@...e.com, josef@...icpanda.com, jack@...e.cz,
ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
michel@...pinasse.org, liam.howlett@...cle.com, jglisse@...gle.com,
vbabka@...e.cz, minchan@...gle.com, dave@...olabs.net,
punit.agrawal@...edance.com, lstoakes@...il.com, hdanton@...a.com,
apopple@...dia.com, peterx@...hat.com, ying.huang@...el.com,
yuzhao@...gle.com, dhowells@...hat.com, hughd@...gle.com,
viro@...iv.linux.org.uk, brauner@...nel.org,
pasha.tatashin@...een.com, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: Re: [PATCH v7 0/6] Per-VMA lock support for swap and userfaults
>>>> Which ends up being
>>>>
>>>> VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
>>>>
>>>> I did not check if this is also the case on mainline, and if this series is responsible.
>>>
>>> Thanks for reporting! I'm checking it now.
>>
>> Hmm. From the code it's not obvious how lock_mm_and_find_vma() ends up
>> calling find_vma() without mmap_lock after successfully completing
>> get_mmap_lock_carefully(). lock_mm_and_find_vma+0x3f/0x270 points to
>> the first invocation of find_vma(), so this is not even the lock
>> upgrade path... I'll try to reproduce this issue and dig up more but
>> from the information I have so far this issue does not seem to be
>> related to this series.
I just checked on mainline and it does not fail there.
>
> This is really weird. I added mmap_assert_locked(mm) calls into
> get_mmap_lock_carefully() right after we acquire mmap_lock read lock
> and one of them triggers right after successful
> mmap_read_lock_killable(). Here is my modified version of
> get_mmap_lock_carefully():
>
> static inline bool get_mmap_lock_carefully(struct mm_struct *mm,
> struct pt_regs *regs) {
> /* Even if this succeeds, make it clear we might have slept */
> if (likely(mmap_read_trylock(mm))) {
> might_sleep();
> mmap_assert_locked(mm);
> return true;
> }
> if (regs && !user_mode(regs)) {
> unsigned long ip = instruction_pointer(regs);
> if (!search_exception_tables(ip))
> return false;
> }
> if (!mmap_read_lock_killable(mm)) {
> mmap_assert_locked(mm); <---- generates a BUG
> return true;
> }
> return false;
> }
Ehm, that's indeed weird.
>
> AFAIKT conditions for mmap_read_trylock() and
> mmap_read_lock_killable() are checked correctly. Am I missing
> something?
Weirdly enough, it only triggers during that specific uffd test, right?
--
Cheers,
David / dhildenb
Powered by blists - more mailing lists