linux-ext4 - Re: [PATCH] ext4: Add checks to xattr code that we have appropriate reclaim context

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Date:   Fri, 5 Mar 2021 09:29:35 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Add checks to xattr code that we have appropriate
 reclaim context

On Mon, Feb 22, 2021 at 06:16:26PM +0100, Jan Kara wrote:
> Syzbot is reporting that ext4 can enter fs reclaim from kvmalloc() while
> the transaction is started like:
> 
>   fs_reclaim_acquire+0x117/0x150 mm/page_alloc.c:4340
>   might_alloc include/linux/sched/mm.h:193 [inline]
>   slab_pre_alloc_hook mm/slab.h:493 [inline]
>   slab_alloc_node mm/slub.c:2817 [inline]
>   __kmalloc_node+0x5f/0x430 mm/slub.c:4015
>   kmalloc_node include/linux/slab.h:575 [inline]
>   kvmalloc_node+0x61/0xf0 mm/util.c:587
>   kvmalloc include/linux/mm.h:781 [inline]
>   ext4_xattr_inode_cache_find fs/ext4/xattr.c:1465 [inline]
>   ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1508 [inline]
>   ext4_xattr_set_entry+0x1ce6/0x3780 fs/ext4/xattr.c:1649
>   ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224
>   ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380
>   ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493
> 
> This should be impossible since transaction start sets PF_MEMALLOC_NOFS.
> Add some assertions to the code to catch if something isn't working as
> expected early.
> 
> Link: https://lore.kernel.org/linux-ext4/000000000000563a0205bafb7970@google.com/
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

					- Ted