Created attachment 1435776 [details]
C program which calls the syscall getdents64 with the given buffer size

Description of problem:
When a program written in Go is listing directory contents in a CIFS mount with many files, the Linux kernel misses some files. When we increase the buffer size for getdents we get a proper listing and no files are lost. 


Version-Release number of selected component (if applicable):
3.10.0-862.el7.x86_64

golang-src-1.9.4-1.el7.noarch
cifs-utils-6.2-10.el7.x86_64
golang-1.9.4-1.el7.x86_64
golang-bin-1.9.4-1.el7.x86_64

How reproducible:
Always 


Steps to Reproduce:
1. mount -t cifs //cifs-server/cifs /mnt 
2. touch /mnt/{1..1000}
3. ls -la /mnt | wc -l 
4. go run man.go /mnt
5. ./man.o 4096 /mnt 


Actual results:

# ls -la /mnt | wc -l 
1003


# go run man.go /mnt
996

# ./getdents_ls 4096 /cifs | tail -n 1 
Found 996 entries

Expected results:

# ls -la /mnt | wc -l 
1003


# go run man.go /mnt
1002

# ./getdents_ls 4096 /cifs | tail -n 1 
Found 1002 entries

Additional info:

I've attached the c program, 


C program. 
----------
 # gcc -Wall getdents_ls.c -o getdents_ls
 # getdents_ls [<buf_size> [<path>]]


GO program. 
----------

 # cat man.go 

package main

import (
        "fmt"
        "os"
)

func main() {
        f, err := os.Open(os.Args[1])
        if err != nil {
                panic(err)
        }
        names, err := f.Readdirnames(-1)
        if err != nil {
                panic(err)
        }
        fmt.Printf("%d\n", len(names)+2 /* ., .. */)
}

 # go run man.go [<path>]]


github issue for more information:  https://github.com/golang/go/issues/24015#issuecomment-369719030