Re: [PATCH] fuse: fix the deadlock in race of reclaim path with kswapd

Kassey Li <quic_yingangl@xxxxxxxxxxx> · Tue, 6 Sep 2022 08:29:11 +0800

On 9/5/2022 9:28 PM, Miklos Szeredi wrote:
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 for this info.

Thanks,
Miklos