A recent regression (introduced after 2.6.21) was caught by the LTP test fcntl11. It appears that F_GETLK is not properly checking for existing F_RDLCK and allows taking out a write lock.
This can be demonstrated by either running fcntl11 from the LTP suite or I have hacked up a much shorter version which demonstrates the issue and am attaching it. Using git bisect I came up with this commit as the one that introduced the issue. I briefly tried to back this out from the current tree but appears a lot has change since then so I will need to try that manually. commit c2fa1b8a6c059dd08a802545fed3badc8df2adc1 Author: J. Bruce Fields <[EMAIL PROTECTED]> Date: Tue Feb 20 16:10:11 2007 -0500 locks: create posix-to-flock helper functions Factor out a bit of messy code by creating posix-to-flock counterparts to the existing flock-to-posix helper functions. Cc: Christoph Hellwig <[EMAIL PROTECTED]> Signed-off-by: "J. Bruce Fields" <[EMAIL PROTECTED]> - Doug
#include <stdio.h> #include <stdlib.h> #include <fcntl.h> #include <errno.h> #include <string.h> #define PATH_MAX 80 #define STRING "abcdefghijklmnopqrstuvwxyz\n" int fd; char *locktypes[] = { "F_RDLCK", "F_WRLCK", "F_UNLCK" }; int do_lock (int cmd, short type, short whence, int start, int len) { struct flock fl; fl.l_type = type; fl.l_whence = whence; fl.l_start = start; fl.l_len = len; return (fcntl (fd, cmd, &fl)); } int test_lock (int type, int start, int len, int expected) { struct flock fl; fflush (stdout); if (fork () == 0) { fl.l_type = type; fl.l_whence = SEEK_SET; fl.l_start = start; fl.l_len = len; fl.l_pid = 0; if (fcntl (fd, F_GETLK, &fl) < 0) { perror ("fcntl"); exit (1); } if (fl.l_type == expected) { printf ("PASS\n"); } else { printf ("FAILED\n"); printf ("\ttype = %s, expect %s\n", locktypes[fl.l_type], locktypes[expected]); printf ("\tstart = %d\n", fl.l_start); printf ("\tlen = %d\n", fl.l_len); printf ("\tpid = %d\n", fl.l_pid); } exit (0); } else { wait (NULL); } return 0; } main () { char *buf = STRING; char template[PATH_MAX]; struct flock fl; snprintf (template, PATH_MAX, "tempfile.XXXXXX"); if ((fd = mkstemp (template)) < 0) { perror ("mkstemp"); fprintf (stderr, "Couldn't open temp file! errno = %d", errno); exit (1); } if (write (fd, buf, strlen (STRING)) < 0) { perror ("write"); fprintf (stderr, "Couldn't write to temp file! errno = %d", errno); exit (1); } /* * Add a write lock to the middle of the file and a read * at the begining */ if (do_lock (F_SETLK, (short) F_WRLCK, (short) 0, 10, 5) < 0) { fprintf (stderr, "fcntl on file failed, errno =%d", errno); exit (1); } if (do_lock (F_SETLK, (short) F_RDLCK, (short) 0, 1, 5) < 0) { fprintf (stderr, "fcntl on file failed, errno =%d", errno); exit (1); } /* this first test fails */ printf ("child will try to get a F_WRLCK on the same area that the F_RDLCK already exists\n"); printf ("it should reject due to the F_RDLCK\n"); test_lock (F_WRLCK, 1, 5, F_RDLCK); }