X found that 2 read requests from wcfs are indeed pending

As it should be.

grep -w -e '<- qread\>' y.log |awk {'print $6'} |sort >qread.txt
grep -w -e '-> read\>' y.log |awk {'print $6'} |sort >read.txt

root@deco:/home/kirr/src/wendelin/wendelin.core/wcfs# xdiff qread.txt read.txt
diff --git a/qread.txt b/read.txt
index 4ab50d7..fdd2be1 100644
--- a/qread.txt
+++ b/read.txt
@@ -53,7 +53,5 @@ wcfs/11399_1_r:
 wcfs/11399_2_r:
 wcfs/11399_3_r:
 wcfs/11399_4_r:
-wcfs/11399_5_r:
 wcfs/11400_0_r:
 wcfs/11401_0_r:
-wcfs/11401_1_r:

root@deco:/home/kirr/src/wendelin/wendelin.core/wcfs# tail -80 y.log
        github.com/hanwen/go-fuse/fuse.handleEINTR+39
        github.com/hanwen/go-fuse/fuse.(*Server).readRequest+355
        github.com/hanwen/go-fuse/fuse.(*Server).loop+107
        runtime.goexit+1

P2 2.215810 /dev/fuse -> read       wcfs/11399_4_r:
        .56  RELEASE i8 ...             (ret=64)

P2 2.215859 /dev/fuse <- write      wcfs/11399_5_w:
        .56 (0) ...

        syscall.Syscall+48
        syscall.Write+73
        github.com/hanwen/go-fuse/fuse.(*Server).systemWrite.func1+76
        github.com/hanwen/go-fuse/fuse.handleEINTR+39
        github.com/hanwen/go-fuse/fuse.(*Server).systemWrite+931
        github.com/hanwen/go-fuse/fuse.(*Server).write+194
        github.com/hanwen/go-fuse/fuse.(*Server).handleRequest+179
        github.com/hanwen/go-fuse/fuse.(*Server).loop+399
        runtime.goexit+1

P2 2.215871 /dev/fuse -> write_ack  wcfs/11399_5_w (ret=16)

P2 2.215876 /dev/fuse <- qread      wcfs/11399_5_r:				<-- NOTE

        syscall.Syscall+48
        syscall.Read+73
        github.com/hanwen/go-fuse/fuse.(*Server).readRequest.func1+85
        github.com/hanwen/go-fuse/fuse.handleEINTR+39
        github.com/hanwen/go-fuse/fuse.(*Server).readRequest+355
        github.com/hanwen/go-fuse/fuse.(*Server).loop+107
        runtime.goexit+1

P0 2.221527 /dev/fuse <- qread      wcfs/11401_1_r:				<-- NOTE

        syscall.Syscall+48
        syscall.Read+73
        github.com/hanwen/go-fuse/fuse.(*Server).readRequest.func1+85
        github.com/hanwen/go-fuse/fuse.handleEINTR+39
        github.com/hanwen/go-fuse/fuse.(*Server).readRequest+355
        github.com/hanwen/go-fuse/fuse.(*Server).loop+107
        runtime.goexit+1

P1 2.239384 /dev/fuse -> read       wcfs/11398_6_r:
        .57  READ i5 ...                (ret=80)

P0 2.239626 /dev/fuse <- write      wcfs/11397_0_w:
        NOTIFY_RETRIEVE ...

        syscall.Syscall+48
        syscall.Write+73
        github.com/hanwen/go-fuse/fuse.(*Server).systemWrite.func1+76
        github.com/hanwen/go-fuse/fuse.handleEINTR+39
        github.com/hanwen/go-fuse/fuse.(*Server).systemWrite+931
        github.com/hanwen/go-fuse/fuse.(*Server).write+194
        github.com/hanwen/go-fuse/fuse.(*Server).InodeRetrieveCache+764
        github.com/hanwen/go-fuse/fuse/nodefs.(*FileSystemConnector).FileRetrieveCache+157
        main.(*BigFile).invalidateBlk+232
        main.(*Root).zδhandle1.func1+72
        golang.org/x/sync/errgroup.(*Group).Go.func1+87
        runtime.goexit+1

P0 2.239660 /dev/fuse -> write_ack  wcfs/11397_0_w (ret=48)

pending read/write:

...

wcfs/fusetrace

@@ -154,6 +154,7 @@ kretprobe::fuse_dev_read {
 
 	$op = @opcode[$h->opcode];
 	printf("P%d %d.%d /dev/fuse -> read       %s/%d_%d_r:\n", cpu, $trr/1000000, $trr%1000000, comm, tid, $rr);
+	// XXX ret=... ^^^
 	printf("\t.%d  %s i%d ...\t\t(ret=%d)\n\n", $h->unique, $op, $h->nodeid, retval);
 }