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Date:   Fri, 11 Jun 2021 20:14:20 +0800
From:   chenguanyou <>
Subject: Re:[PATCH] fuse: alloc_page nofs avoid deadlock

PID: 9652 TASK: ffffffc0c9ce0000 CPU: 4 COMMAND: "kworker/u16:8"
#0 [ffffff802e793650] __switch_to at ffffff8008086a4c
#1 [ffffff802e7936c0] __schedule at ffffff80091ffe58
#2 [ffffff802e793720] schedule at ffffff8009200348
#3 [ffffff802e793770] __fuse_request_send at ffffff8008435760
#4 [ffffff802e7937b0] fuse_simple_request at ffffff8008435b14
#5 [ffffff802e793930] fuse_flush_times at ffffff800843a7a0
#6 [ffffff802e793950] fuse_write_inode at ffffff800843e4dc
#7 [ffffff802e793980] __writeback_single_inode at ffffff8008312740
#8 [ffffff802e793aa0] writeback_sb_inodes at ffffff80083117e4
#9 [ffffff802e793b00] __writeback_inodes_wb at ffffff8008311d98
#10 [ffffff802e793c00] wb_writeback at ffffff8008310cfc
#11 [ffffff802e793d00] wb_workfn at ffffff800830e4a8
#12 [ffffff802e793d90] process_one_work at ffffff80080e4fac
#13 [ffffff802e793e00] worker_thread at ffffff80080e5670
#14 [ffffff802e793e60] kthread at ffffff80080eb650

crash> p __writeback_single_inode
__writeback_single_inode = $119 =
{int (struct inode *, struct writeback_control *)} 0xffffff8008312040 <__writeback_single_inode>

0xffffff8008312040 <__writeback_single_inode>: stp x29, x30, [sp,#-96]!
0xffffff8008312044 <__writeback_single_inode+4>: stp x28, x27, [sp,#16]
0xffffff8008312048 <__writeback_single_inode+8>: stp x26, x25, [sp,#32]
0xffffff800831204c <__writeback_single_inode+12>: stp x24, x23, [sp,#48]
0xffffff8008312050 <__writeback_single_inode+16>: stp x22, x21, [sp,#64]
0xffffff8008312054 <__writeback_single_inode+20>: stp x20, x19, [sp,#80]
0xffffff8008312058 <__writeback_single_inode+24>: mov x29, sp

0xffffff8008311374 <writeback_sb_inodes>: sub sp, sp, #0x120
0xffffff8008311378 <writeback_sb_inodes+4>: stp x29, x30, [sp,#192]
0xffffff800831137c <writeback_sb_inodes+8>: stp x28, x27, [sp,#208]
0xffffff8008311380 <writeback_sb_inodes+12>: stp x26, x25, [sp,#224]
0xffffff8008311384 <writeback_sb_inodes+16>: stp x24, x23, [sp,#240]
0xffffff8008311388 <writeback_sb_inodes+20>: stp x22, x21, [sp,#256]
0xffffff800831138c <writeback_sb_inodes+24>: stp x20, x19, [sp,#272]
0xffffff8008311390 <writeback_sb_inodes+28>: add x29, sp, #0xc0

0xffffff80083117d8 <writeback_sb_inodes+1124>: add x1, sp, #0x60
0xffffff80083117dc <writeback_sb_inodes+1128>: mov x0, x27
0xffffff80083117e0 <writeback_sb_inodes+1132>: stp x21, xzr, [sp,#96]
0xffffff80083117e4 <writeback_sb_inodes+1136>: bl 0xffffff8008312040 <__writeback_single_inode>

x27 = inode,sp + 0x60 = writeback_control

#7 [ffffff802e793980] __writeback_single_inode at ffffff8008312740
ffffff802e793980: ffffff802e793aa0 ffffff80083117e8
ffffff802e793990: ffffffc0791dd1c8 ffffffc0791dd140

so : #7 [ffffff802e793980] __writeback_single_inode(0xffffffc0791dd140, 0xffffff802e793a40) at ffffff8008312740

crash> p __fuse_request_send
__fuse_request_send = $124 =
{void (struct fuse_conn *, struct fuse_req *)} 0xffffff8008435604 <__fuse_request_send>

0xffffff8008435604 <__fuse_request_send>: sub sp, sp, #0x70
0xffffff8008435608 <__fuse_request_send+4>: stp x29, x30, [sp,#48]
0xffffff800843560c <__fuse_request_send+8>: stp x24, x23, [sp,#64]
0xffffff8008435610 <__fuse_request_send+12>: stp x22, x21, [sp,#80]
0xffffff8008435614 <__fuse_request_send+16>: stp x20, x19, [sp,#96]
0xffffff8008435618 <__fuse_request_send+20>: add x29, sp, #0x3

0xffffff8008435b0c <fuse_simple_request+368>: mov x0, x19
0xffffff8008435b10 <fuse_simple_request+372>: mov x1, x20
0xffffff8008435b14 <fuse_simple_request+376>: bl 0xffffff8008435604 <__fuse_request_send>

x19 = fuse_conn,x20 = fuse_req

#3 [ffffff802e793770] __fuse_request_send at ffffff8008435760
ffffff802e793770: ffffff802e7937b0 ffffff8008435b18
ffffff802e793780: ffffffc0791dd1c8 ffffffc0c9ce0000
ffffff802e793790: ffffffc0c6feb1f8 ffffff802e7938b8
ffffff802e7937a0: ffffffc0c6feb148 ffffffc0901f2f80

#3 [ffffff802e793770] __fuse_request_send(0xffffffc0901f2f80, 0xffffffc0c6feb148) at ffffff8008435760

crash> struct -x fuse_req.flags ffffffc0c6feb148
flags = 0x9  = 0000 0000 1001  ===>> FR_WAITING | FR_ISREPLY


PID: 17172 TASK: ffffffc0c162c000 CPU: 6 COMMAND: "Thread-21"
#0 [ffffff802d16b400] __switch_to at ffffff8008086a4c
#1 [ffffff802d16b470] __schedule at ffffff80091ffe58
#2 [ffffff802d16b4d0] schedule at ffffff8009200348
#3 [ffffff802d16b4f0] bit_wait at ffffff8009201098
#4 [ffffff802d16b510] __wait_on_bit at ffffff8009200a34
#5 [ffffff802d16b5b0] inode_wait_for_writeback at ffffff800830e1e8
#6 [ffffff802d16b5e0] evict at ffffff80082fb15c
#7 [ffffff802d16b620] iput at ffffff80082f9270
#8 [ffffff802d16b680] dentry_unlink_inode at ffffff80082f4c90
#9 [ffffff802d16b6a0] __dentry_kill at ffffff80082f1710
#10 [ffffff802d16b6d0] shrink_dentry_list at ffffff80082f1c34
#11 [ffffff802d16b750] prune_dcache_sb at ffffff80082f18a8
#12 [ffffff802d16b770] super_cache_scan at ffffff80082d55ac
#13 [ffffff802d16b860] shrink_slab at ffffff8008266170
#14 [ffffff802d16b900] shrink_node at ffffff800826b420
#15 [ffffff802d16b980] do_try_to_free_pages at ffffff8008268460
#16 [ffffff802d16ba60] try_to_free_pages at ffffff80082680d0
#17 [ffffff802d16bbe0] __alloc_pages_nodemask at ffffff8008256514
#18 [ffffff802d16bc60] fuse_copy_fill at ffffff8008438268
#19 [ffffff802d16bd00] fuse_dev_do_read at ffffff8008437654
#20 [ffffff802d16bdc0] fuse_dev_splice_read at ffffff8008436f40
#21 [ffffff802d16be60] sys_splice at ffffff8008315d18
#22 [ffffff802d16bff0] __sys_trace at ffffff8008084014

crash> p fuse_dev_do_read
fuse_dev_do_read = $259 = 
 {ssize_t (struct fuse_dev *, struct file *, struct fuse_copy_state *, size_t)} 0xffffff8008437170 <fuse_dev_do_read>

0xffffff8008437650 <fuse_dev_do_read+1248>: mov x0, x19
0xffffff8008437654 <fuse_dev_do_read+1252>: bl 0xffffff8008438110 <fuse_copy_fill>

0xffffff8008438110 <fuse_copy_fill>: sub sp, sp, #0x50
0xffffff8008438114 <fuse_copy_fill+4>: stp x29, x30, [sp,#32]
0xffffff8008438118 <fuse_copy_fill+8>: str x21, [sp,#48]
0xffffff800843811c <fuse_copy_fill+12>: stp x20, x19, [sp,#64]
0xffffff8008438120 <fuse_copy_fill+16>: add x29, sp, #0x20

#18 [ffffff802d16bc60] fuse_copy_fill at ffffff8008438268
ffffff802d16bc60: ffffff802d16bd00 ffffff8008437658
ffffff802d16bc70: 0000000000000028 ffffff8008437620
ffffff802d16bc80: ffffffc0901f2f80 ffffff802d16bd68   // fuse_copy_state

#4 [ffffff802d16bd00] fuse_dev_do_read(ffffffc0af775e00, ffffffc07ab65340, ffffff802d16bd68 ,0000000000021000) at ffffff8008437654

crash> struct -x fuse_copy_state ffffff802d16bd68
struct fuse_copy_state {
write = 0x1,
req = 0xffffffc0c6feb148,   // #3 [ffffff802e793770] __fuse_request_send(ffffffc0901f2f80, ffffffc0c6feb148) at ffffff8008435760
iter = 0x0, 
pipebufs = 0xffffffc0d1dd2000,
currbuf = 0x0,
pipe = 0xffffffc015bd7440,
nr_segs = 0x0,
pg = 0x0,
len = 0x0,
offset = 0x0,
move_pages = 0x0

0xffffff80082fb158 <evict+156>: mov x0, x19
0xffffff80082fb15c <evict+160>: bl 0xffffff800830e14c <inode_wait_for_writeback>

crash> p inode_wait_for_writeback
inode_wait_for_writeback = $107 =
{void (struct inode *)} 0xffffff800830e14c <inode_wait_for_writeback>

x19 = inode

crash> dis inode_wait_for_writeback
0xffffff800830e14c <inode_wait_for_writeback>: sub sp, sp, #0x80
0xffffff800830e150 <inode_wait_for_writeback+4>: stp x29, x30, [sp,#80]
0xffffff800830e154 <inode_wait_for_writeback+8>: stp x22, x21, [sp,#96]
0xffffff800830e158 <inode_wait_for_writeback+12>: stp x20, x19, [sp,#112]
0xffffff800830e15c <inode_wait_for_writeback+16>: add x29, sp, #0x50

#5 [ffffff802d16b5b0] inode_wait_for_writeback at ffffff800830e1e8
x19 = sp + 0x78 ===>>  x29 + 0x28 = ffffff802d16b5b0 + 0x28 = ffffff802d16b5d8

crash> rd ffffff802d16b5d8
ffffff802d16b5d8: ffffffc0791dd140 @..y.

crash> struct -x inode.i_state ffffffc0791dd140
i_state = 0xa0  = 1010 0000 = I_SYNC | I_FREEING


                 9652                                                   17172
__fuse_request_send(ffffffc0901f2f80, ffffffc0c6feb148)
               ...                                              fuse_dev_do_read
	   	request_wait_answer   <<=========================				...
														|	|=> inode_wait_for_writeback
 inode_sync_complete(0xffffffc0791dd140) ===============|==>| wake up 17172		
                                                        |<<== request_end(xxx, 0xffffffc0c6feb148) wake up 9652

static unsigned long super_cache_scan(struct shrinker *shrink,
                      struct shrink_control *sc)
     * Deadlock avoidance.  We may hold various FS locks, and we don't want
     * to recurse into the FS that called us in clear_inode() and friends..
    if (!(sc->gfp_mask & __GFP_FS))   // page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
        return SHRINK_STOP;

static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
                    nodemask_t *nodemask)
     * If the caller cannot enter the filesystem, it's possible that it
     * is due to the caller holding an FS lock or performing a journal
     * transaction in the case of a filesystem like ext[3|4]. In this case,
     * it is not safe to block on pfmemalloc_wait as kswapd could be
     * blocked waiting on the same lock. Instead, throttle for up to a
     * second before continuing.
    if (!(gfp_mask & __GFP_FS)) {
            allow_direct_reclaim(pgdat), HZ);

        goto check_pending;

    /* Throttle until kswapd wakes the process */

The fix will cause other problems?


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