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

[Kassey Li]

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

Suggested-by: Wang Mao <quic_maow@xxxxxxxxxxx>
Signed-off-by: Kassey Li <quic_yingangl@xxxxxxxxxxx>
---
 fs/fuse/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 51897427a534..0df7234840c3 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -713,7 +713,7 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
 			if (cs->nr_segs >= cs->pipe->max_usage)
 				return -EIO;
 
-			page = alloc_page(GFP_HIGHUSER);
+			page = alloc_page(GFP_HIGHUSER & ~__GFP_FS);
 			if (!page)
 				return -ENOMEM;
 
-- 
2.17.1