Regression on linux-next (next-20240712)

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

Hello Pei,

Hope you are doing well. I am Chaitanya from the linux graphics team in Intel.

This mail is regarding a regression we are seeing in our CI runs[1] on linux-next repository.

In version next-20240712[2], we saw the following regression (currently being masked by another regression)

`````````````````````````````````````````````````````````````````````````````````
<4>[   14.530533] ============================================
<4>[   14.530533] WARNING: possible recursive locking detected
<4>[   14.530534] 6.10.0-rc7-next-20240712-next-20240712-g3fe121b62282+ #1 Not tainted
<4>[   14.530535] --------------------------------------------
<4>[   14.530535] (direxec)/171 is trying to acquire lock:
<4>[   14.530536] ffff8881010725d8 (&mm->mmap_lock){++++}-{3:3}, at: unmap_single_vma+0xea/0x170
<4>[   14.530541] 
                  but task is already holding lock:
<4>[   14.530542] ffff8881010725d8 (&mm->mmap_lock){++++}-{3:3}, at: exit_mmap+0x6a/0x450
<4>[   14.530545] 
                  other info that might help us debug this:
<4>[   14.530545]  Possible unsafe locking scenario:
`````````````````````````````````````````````````````````````````````````````````
Details log can be found in [3].

After bisecting the tree, the following patch [4] seems to be the first "bad"
commit

`````````````````````````````````````````````````````````````````````````````````````````````````````````
commit a13252049629a8225f38a9be7d8d4fc4ff5350e8
Author: Pei Li mailto:peili.dev@gmail.com
Date:   Wed Jul 10 22:13:17 2024 -0700

    mm: fix mmap_assert_locked() in follow_pte()

`````````````````````````````````````````````````````````````````````````````````````````````````````````

We also verified that if we revert the patch the issue is not seen.

Could you please check why the patch causes this regression and provide a fix if necessary?

Thank you.

Regards

Chaitanya

[1] https://intel-gfx-ci.01.org/tree/linux-next/combined-alt.html?
[2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20240712 
[3] https://gfx-ci.igk.intel.com/tree/linux-next/next-20240712/bat-arlh-2/boot0.txt
[4] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20240712&id=a13252049629a8225f38a9be7d8d4fc4ff5350e8