Bug 1069393

Description of problem:

With a kernel config that does not include CONFIG_SWAP, /proc/swaps does not exist.  systemd-208-14.fc20 segfaults while enumerating swap devices in this case.  systemd-208-9.fc20 worked.

Version-Release number of selected component (if applicable):

208-14.fc20

How reproducible:

Reliably.

Steps to Reproduce:
1. Build kernel without CONFIG_SWAP.
2. Install systemd-208-14.fc20
3. Reboot the system or systemctl daemon-reexec

Actual results:

Feb 24 13:10:47 fedora systemd[1]: Reexecuting.
Feb 24 13:10:47 fedora systemd[1]: systemd 208 running in system mode. (+PAM +LIBWRAP +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ)
Feb 24 13:10:47 fedora systemd[1]: Detected virtualization 'kvm'.
Feb 24 13:10:48 fedora kernel: systemd[1]: segfault at 0 ip 00007f047f4f0b61 sp 00007fff60cd4b50 error 4 in libc-2.18.so[7f047f47c000+1b4000]
Feb 24 13:10:48 fedora systemd[1]: Caught <SEGV>, dumped core as pid 7646.
Feb 24 13:10:48 fedora systemd[1]: Freezing execution.

Expected results:

Feb 24 14:17:32 fedora systemd[1]: Reexecuting.
Feb 24 14:17:32 fedora systemd[1]: systemd 208 running in system mode. (+PAM +LIBWRAP +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ)
Feb 24 14:17:32 fedora systemd[1]: Detected virtualization 'kvm'.

Additional info:

Backtrace is:
(gdb) bt
#0  0x00007f047f84a62b in raise (sig=sig@entry=11) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:37
#1  0x00007f04813959ae in crash (sig=11) at ../src/core/main.c:152
#2  <signal handler called>
#3  __GI_rewind (fp=0x0) at rewind.c:35
#4  0x00007f04813b6fee in swap_load_proc_swaps (m=m@entry=0x7f04822f9560, set_flags=set_flags@entry=false) at ../src/core/swap.c:1033
#5  0x00007f04813b7361 in swap_enumerate (m=0x7f04822f9560) at ../src/core/swap.c:1255
#6  0x00007f0481398554 in manager_enumerate (m=0x7f04822f9560) at ../src/core/manager.c:789
#7  0x00007f048139afdc in manager_startup (m=0x7f04822f9560, serialization=0x7f04822ef2c0, fds=0x7f04822f7550) at ../src/core/manager.c:905
#8  0x00007f0481393827 in main (argc=4, argv=0x7fff60cd5578) at ../src/core/main.c:1583

It looks like the refactoring in SOURCES/0147-core-do-not-segfault-if-swap-activity-happens-when-p.patch has caused swap_enumerate to continue if fopen() sets errno=ENOENT.  Previously, the error would cause swap_enumerate to terminate successfully, but now it is open_proc_swaps that completes "successfully".  Both swap_dispatch_reload and swap_enumerate continue even though m->proc_swaps is NULL.