Re: xfs : WARNING: possible circular locking dependency detected

[Xiubo Li]

On 4/18/24 13:04, Dave Chinner wrote:
> On Thu, Apr 18, 2024 at 11:39:25AM +0800, Xiubo Li wrote:
> > Hi all
> >
> > BTW, is this a known issue and has it been fixed already ? I can reproduce
> > this always with my VMs:
> >
> >
> > <4>[ 9009.171195]
> > <4>[ 9009.171205] ======================================================
> > <4>[ 9009.171208] WARNING: possible circular locking dependency detected
> > <4>[ 9009.171211] 6.9.0-rc3+ #49 Not tainted
> > <4>[ 9009.171214] ------------------------------------------------------
> > <4>[ 9009.171216] kswapd0/149 is trying to acquire lock:
> > <4>[ 9009.171219] ffff88811346a920 (&xfs_nondir_ilock_class){++++}-{4:4},
> > at: xfs_reclaim_inode+0x3ac/0x590 [xfs]
> > <4>[ 9009.171580]
> > <4>[ 9009.171580] but task is already holding lock:
> > <4>[ 9009.171583] ffffffff8bb33100 (fs_reclaim){+.+.}-{0:0}, at:
> > balance_pgdat+0x5d9/0xad0
> > <4>[ 9009.171593]
> > <4>[ 9009.171593] which lock already depends on the new lock.
> > <4>[ 9009.171593]
> > <4>[ 9009.171595]
> > <4>[ 9009.171595] the existing dependency chain (in reverse order) is:
> > <4>[ 9009.171597]
> > <4>[ 9009.171597] -> #1 (fs_reclaim){+.+.}-{0:0}:
> > <4>[ 9009.171603]        __lock_acquire+0x7da/0x1030
> > <4>[ 9009.171610]        lock_acquire+0x15d/0x400
> > <4>[ 9009.171614]        fs_reclaim_acquire+0xb5/0x100
> > <4>[ 9009.171618] prepare_alloc_pages.constprop.0+0xc5/0x230
> > <4>[ 9009.171622]        __alloc_pages+0x12a/0x3f0
> > <4>[ 9009.171625]        alloc_pages_mpol+0x175/0x340
> > <4>[ 9009.171630]        stack_depot_save_flags+0x4c5/0x510
> > <4>[ 9009.171635]        kasan_save_stack+0x30/0x40
> > <4>[ 9009.171640]        kasan_save_track+0x10/0x30
> > <4>[ 9009.171643]        __kasan_slab_alloc+0x83/0x90
> > <4>[ 9009.171646]        kmem_cache_alloc+0x15e/0x4a0
> > <4>[ 9009.171652]        __alloc_object+0x35/0x370
> > <4>[ 9009.171659]        __create_object+0x22/0x90
> > <4>[ 9009.171665] __kmalloc_node_track_caller+0x477/0x5b0
> > <4>[ 9009.171672]        krealloc+0x5f/0x110
> > <4>[ 9009.171679]        xfs_iext_insert_raw+0x4b2/0x6e0 [xfs]
> > <4>[ 9009.172172]        xfs_iext_insert+0x2e/0x130 [xfs]
> The only krealloc() in this path is:
>
> 	new = krealloc(ifp->if_data, new_size,
>                          GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOFAIL);
>
> And it explicitly uses __GFP_NOLOCKDEP to tell lockdep not to warn
> about this allocation because of this false positive situation.
>
> Oh. I've seen this before. This is a KASAN bug, and I'm pretty sure
> I've posted a patch to fix it a fair while back that nobody seemed
> to care about enough to review or merge it.
>
> That is: kasan_save_stack() is doing a fixed GFP_KERNEL allocation
> in an context where GFP_KERNEL allocations are known to generate
> lockdep false positives.  This occurs depsite the XFS and general
> memory allocation code doing exactly the right thing to avoid the
> lockdep false positives (i.e. using and obeying __GFP_NOLOCKDEP).
>
> The kasan code ends up in stack_depot_save_flags(), which does a
> GFP_KERNEL allocation but filters out __GFP_NOLOCKDEP and does not
> add it back. Hence kasan generates the false positive lockdep
> warnings, not the code doing the original allocation.
>
> kasan and/or stack_depot_save_flags() needs fixing here.

Hi Dave,

Thanks very much for your feedback.

BTW, do you have the link of your patch ? I can help test it.

Thanks

- Xiubo


> -Dave.