On Mon, 5 Sept 2022 at 09:17, Kassey Li <quic_yingangl@xxxxxxxxxxx> wrote:
>
> Task A wait for writeback, while writeback Task B send request to fuse.
> Task C is expected to serve this request, here it is in direct reclaim
> path cause deadlock when system is in low memory.
>
> without __GFP_FS in Task_C break throttle_direct_reclaim with an
> HZ timeout.
>
> kswpad (Task_A): writeback(Task_B):
> __switch_to+0x14c schedule+0x70
> __schedule+0xb5c __fuse_request_send+0x154
> schedule+0x70 fuse_simple_request+0x184
> bit_wait+0x18 fuse_flush_times+0x114
> __wait_on_bit+0x74 fuse_write_inode+0x60
> inode_wait_for_writeback+0xa4 __writeback_single_inode+0x3d8
> evict+0xa8 writeback_sb_inodes+0x4c0
> iput+0x248 __writeback_inodes_wb+0xb0
> dentry_unlink_inode+0xdc wb_writeback+0x270
> __dentry_kill[jt]+0x110 wb_workfn+0x37c
> shrink_dentry_list+0x17c process_one_work+0x284
> prune_dcache_sb+0x5c
> super_cache_scan+0x11c
> do_shrink_slab+0x248
> shrink_slab+0x260
> shrink_node+0x678
> kswapd+0x8ec
> kthread+0x140
> ret_from_fork+0x10
>
> Task_C:
> __switch_to+0x14c
> __schedule+0xb5c
> schedule+0x70
> throttle_direct_reclaim
> try_to_free_pages
> __perform_reclaim
> __alloc_pages_direct_reclaim
> __alloc_pages_slowpath
> __alloc_pages_nodemask
> alloc_pages
> fuse_copy_fill+0x168
> fuse_dev_do_read+0x37c
> fuse_dev_splice_read+0x94
Should already be fixed in v5.16 by commit 5c791fe1e2a4 ("fuse: make
sure reclaim doesn't write the inode").
Thanks,
Miklos
