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Anders Kaseorg b9311277c2 fifo: Do not restart open() if it already found a partner 
commit 05d290d66b upstream.

If a parent and child process open the two ends of a fifo, and the
child immediately exits, the parent may receive a SIGCHLD before its
open() returns.  In that case, we need to make sure that open() will
return successfully after the SIGCHLD handler returns, instead of
throwing EINTR or being restarted.  Otherwise, the restarted open()
would incorrectly wait for a second partner on the other end.

The following test demonstrates the EINTR that was wrongly thrown from
the parent’s open().  Change .sa_flags = 0 to .sa_flags = SA_RESTART
to see a deadlock instead, in which the restarted open() waits for a
second reader that will never come.  (On my systems, this happens
pretty reliably within about 5 to 500 iterations.  Others report that
it manages to loop ~forever sometimes; YMMV.)

  #include <sys/stat.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  #include <fcntl.h>
  #include <signal.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>

  #define CHECK(x) do if ((x) == -1) {perror(#x); abort();} while(0)

  void handler(int signum) {}

  int main()
  {
      struct sigaction act = {.sa_handler = handler, .sa_flags = 0};
      CHECK(sigaction(SIGCHLD, &act, NULL));
      CHECK(mknod("fifo", S_IFIFO | S_IRWXU, 0));
      for (;;) {
          int fd;
          pid_t pid;
          putc('.', stderr);
          CHECK(pid = fork());
          if (pid == 0) {
              CHECK(fd = open("fifo", O_RDONLY));
              _exit(0);
          }
          CHECK(fd = open("fifo", O_WRONLY));
          CHECK(close(fd));
          CHECK(waitpid(pid, NULL, 0));
      }
  }

This is what I suspect was causing the Git test suite to fail in
t9010-svn-fe.sh:

	http://bugs.debian.org/678852

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2012-07-19 08:58:56 -07:00
..
9p 9p changes for the 3.4 merge window 2012-03-28 09:58:38 -07:00
adfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
affs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
afs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
autofs4 autofs: make the autofsv5 packet file descriptor use a packetized pipe 2012-04-29 13:30:08 -07:00
befs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
bfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
btrfs Btrfs: run delayed directory updates during log replay 2012-07-16 09:04:05 -07:00
cachefiles switch touch_atime to struct path 2012-03-20 21:29:41 -04:00
ceph Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client 2012-03-28 10:01:29 -07:00
cifs cifs: when server doesn't set CAP_LARGE_READ_X, cap default rsize at MaxBufferSize 2012-07-16 09:03:54 -07:00
coda Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
configfs make configfs_pin_fs() return root dentry on success 2012-03-20 21:29:48 -04:00
cramfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
debugfs simple_open: automatically convert to simple_open() 2012-04-05 15:25:50 -07:00
devpts Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
dlm dlm fixes for 3.4 2012-04-23 18:22:42 -07:00
ecryptfs eCryptfs: Properly check for O_RDONLY flag before doing privileged open 2012-07-16 09:04:26 -07:00
efs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
exofs exofs: Fix CRASH on very early IO errors. 2012-06-10 00:36:05 +09:00
exportfs
ext2 migrate ext2_fs.h guts to fs/ext2/ext2.h 2012-03-31 16:03:16 -04:00
ext3 ext3: move headers to fs/ext3/ 2012-03-31 16:03:16 -04:00
ext4 ext4: fix the free blocks calculation for ext3 file systems w/ uninit_bg 2012-06-17 11:21:23 -07:00
fat fat: fix bug in enforcing Long File Name length 2012-03-23 16:58:40 -07:00
freevxfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
fscache
fuse fuse: fix stat call on 32 bit platforms 2012-06-17 11:21:29 -07:00
gfs2 GFS2: Instruct DLM to avoid queue convert slowdown 2012-04-24 13:26:50 +01:00
hfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
hfsplus hfsplus: fix bless ioctl when used with hardlinks 2012-06-22 11:36:57 -07:00
hostfs Merge branch 'for-linus-3.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml 2012-03-27 18:29:53 -07:00
hpfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
hppfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
hugetlbfs hugetlbfs: lockdep annotate root inode properly 2012-04-25 21:26:34 -07:00
isofs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
jbd Power management updates for 3.4 2012-03-21 10:15:51 -07:00
jbd2 jbd2: use GFP_NOFS for blkdev_issue_flush 2012-04-23 21:43:41 -04:00
jffs2 jffs2: Fix lock acquisition order bug in gc path 2012-05-07 20:30:14 +01:00
jfs jfs: mising cleanup on register_filesystem() failure 2012-03-20 21:29:48 -04:00
lockd SUNRPC: move per-net operations from svc_destroy() 2012-07-16 09:04:39 -07:00
logfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
minix Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
ncpfs Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
nfs NFS: hard-code init_net for NFS callback transports 2012-07-16 09:04:40 -07:00
nfs_common
nfsd SUNRPC: move per-net operations from svc_destroy() 2012-07-16 09:04:39 -07:00
nilfs2 nilfs2: ensure proper cache clearing for gc-inodes 2012-07-16 09:03:51 -07:00
nls
notify fs/notify/notification.c: make subsys_initcall function static 2012-03-23 16:58:31 -07:00
ntfs Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
ocfs2 ocfs2: fix NULL pointer dereference in __ocfs2_change_file_space() 2012-07-16 09:04:45 -07:00
omfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
openpromfs switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
proc vfs: Fix /proc/<tid>/fdinfo/<fd> file handling 2012-06-10 00:36:18 +09:00
pstore Merge branch 'akpm' (Andrew's patch-bomb) 2012-04-05 15:30:34 -07:00
qnx4 qnx4: new helper - try_extent() 2012-03-20 21:29:52 -04:00
qnx6 fs: initial qnx6fs addition 2012-03-20 21:29:38 -04:00
quota Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs 2012-03-28 10:00:14 -07:00
ramfs fs: ramfs: file-nommu: add SetPageUptodate() 2012-07-16 09:04:45 -07:00
reiserfs Disintegrate and delete asm/system.h 2012-03-28 15:58:21 -07:00
romfs MTD merge for 3.4 2012-03-30 17:31:56 -07:00
squashfs Add an extra mount time sanity check, plus some code cleanups and bug fixes. 2012-03-28 18:05:54 -07:00
sysfs sysfs: handle 'parent deleted before child added' 2012-04-10 14:48:51 -07:00
sysv switch open-coded instances of d_make_root() to new helper 2012-03-20 21:29:35 -04:00
ubifs - Improve error messages 2012-03-23 09:27:40 -07:00
udf udf: Fortify loading of sparing table 2012-07-16 09:03:51 -07:00
ufs Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
xfs Disintegrate and delete asm/system.h 2012-03-28 15:58:21 -07:00
aio.c vfs: make AIO use the proper rw_verify_area() area helpers 2012-06-01 15:18:14 +08:00
anon_inodes.c anon_inodes: move allocation of anon_inode into ->mount() 2012-03-20 21:29:45 -04:00
attr.c vfs: increment iversion when a file is truncated 2012-06-10 00:36:12 +09:00
bad_inode.c
binfmt_aout.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_elf.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_elf_fdpic.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_em86.c __register_binfmt() made void 2012-03-20 21:29:46 -04:00
binfmt_flat.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
binfmt_misc.c magic.h: move some FS magic numbers into magic.h 2012-03-23 16:58:31 -07:00
binfmt_script.c __register_binfmt() made void 2012-03-20 21:29:46 -04:00
binfmt_som.c VM: add "vm_mmap()" helper function 2012-04-20 17:29:13 -07:00
bio-integrity.c fs: remove the second argument of k[un]map_atomic() 2012-03-20 21:48:21 +08:00
bio.c bio allocation failure due to bio_get_nr_vecs() 2012-05-11 16:45:12 +02:00
block_dev.c block: don't mark buffers beyond end of disk as mapped 2012-05-11 16:42:14 +02:00
buffer.c block: fix infinite loop in __getblk_slow 2012-07-19 08:58:55 -07:00
char_dev.c
compat.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-03-29 18:12:23 -07:00
compat_binfmt_elf.c
compat_ioctl.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
dcache.c vfs: make word-at-a-time accesses handle a non-existing page 2012-05-03 14:01:40 -07:00
dcookies.c
direct-io.c
drop_caches.c
eventfd.c
eventpoll.c epoll: clear the tfile_check_list on -ELOOP 2012-04-25 21:26:33 -07:00
exec.c mm: correctly synchronize rss-counters at exit/exec 2012-07-16 09:04:08 -07:00
fcntl.c
fhandle.c
fifo.c fifo: Do not restart open() if it already found a partner 2012-07-19 08:58:56 -07:00
file.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-03-29 18:12:23 -07:00
file_table.c vfs: drop_file_write_access() made static 2012-03-20 21:29:32 -04:00
filesystems.c
fs-writeback.c trivial writeback fixes 2012-03-28 10:07:27 -07:00
fs_struct.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
generic_acl.c
inode.c trim includes in inode.c 2012-03-20 21:29:51 -04:00
internal.h
ioctl.c
ioprio.c
Kconfig Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-03-21 13:36:41 -07:00
Kconfig.binfmt
libfs.c dentry leak in simple_fill_super() failure exit 2012-04-09 01:39:22 -04:00
locks.c Remove easily user-triggerable BUG from generic_setlease 2012-07-19 08:58:54 -07:00
Makefile fs: initial qnx6fs addition 2012-03-20 21:29:38 -04:00
mbcache.c
mount.h
mpage.c
namei.c vfs: make word-at-a-time accesses handle a non-existing page 2012-05-03 14:01:40 -07:00
namespace.c vfs: umount_tree() might be called on subtree that had never made it 2012-06-10 00:36:12 +09:00
no-block.c
open.c vfs: make O_PATH file descriptors usable for 'fchdir()' 2012-07-16 09:04:23 -07:00
pipe.c pipes: add a "packetized pipe" mode for writing 2012-04-29 13:12:42 -07:00
pnode.c
pnode.h
posix_acl.c
proc_namespace.c
read_write.c
read_write.h
readdir.c
select.c Merge branch 'x86-x32-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-03-29 18:12:23 -07:00
seq_file.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
signalfd.c
splice.c splice: fix racy pipe->buffers uses 2012-07-16 09:04:42 -07:00
stack.c
stat.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
statfs.c
super.c The following text was taken from the original review request: 2012-03-24 10:24:31 -07:00
sync.c
timerfd.c
utimes.c
xattr.c fs/xattr.c:setxattr(): improve handling of allocation failures 2012-04-05 15:25:50 -07:00
xattr_acl.c