Found during test of 'stress-ng --pseek ...' from current upstream
stress-ng git HEAD:
Testcase:
$ uname -r
3.5.4-1.x86_64
$ cat pfail.c
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
int main()
{
int fd = open("pwrite.tmp", O_RDWR|O_CREAT|O_BINARY, 0666);
if (fd < 0) {
perror("open"); return 1;
}
char c = 42;
if (pwrite(fd, &c, 1, 0) < 0)
perror("pwrite");
if (fork() == 0) {
if (pread(fd, &c, 1, 0) < 0)
perror("pread");
_exit(0);
}
int status;
wait(&status);
return 0;
}
$ make pfail
cc pfail.c -o pfail
$ ./pfail
pread: Bad file descriptor
$ strace ./pfail
...
617 75356 [main] pfail 10826 dofork: 10827 = fork()
82 11289 [main] pfail 10827 seterrno_from_nt_status:
/usr/src/debug/cygwin-3.5.4-1/winsup/cygwin/fhandler/disk_file.cc:1883
status 0xC0000008 -> windows error 6
80 75436 [main] pfail 10826 wait4: calling proc_subproc, pid -1,
options 0
76 11365 [main] pfail 10827 geterrno_from_win_error: windows error
6 == errno 9
78 75514 [main] pfail 10826 proc_subproc: args: 5, -7728
64 11429 [main] pfail 10827 pread: -1 = pread(3, 0x7FFFFCC0B, 1,
0), errno 9
...
The problem does not occur if there is no pread()/pwrite() before the
fork(). This suggests that the child process inherits the extra handle
value used to keep the original seek position, but not the actual handle.
--
Regards,
Christian
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