ALT Linux Bugzilla – #2013

[<a href="mailto:root@sirius" target="_new">root@sirius</a> root]# rpm -q apt rpm
apt-0.5.4cnc9-alt4
rpm-4.0.4-alt12

When doing \&quot;apt-get install XXX\&quot; and the required packages are on more than one CD-ROM (so disk changing is necessary), the operation hangs after fetching all packages.  I have reproduced this on my system (which is only partially upgraded from Sisyphus, and some packages are from Master 2.0 CDs):

[<a href="mailto:root@sirius" target="_new">root@sirius</a> root]# apt-get install libpwlib-devel
Reading Package Lists... Done
Building Dependency Tree... Done
The following extra packages will be installed:
  libpwlib 
The following NEW packages will be installed:
  libpwlib libpwlib-devel 
0 packages upgraded, 2 newly installed, 0 removed and 0 not upgraded.
Need to get 0B/1312kB of archives. After unpacking 4459kB will be used.
Do you want to continue? [Y/n] 
Media Change: Please insert the disc labeled \'ALT Linux Master CD 1\' in the drive \'/mnt/cdrom/\' and press enter

Get:1 <a href="cdrom://ALT">cdrom://ALT</a> Linux Master CD 1 Mandrake/Master libpwlib 1.2.12-alt1 [918kB]
Fetched 918kB in 16s (54.1kB/s)
Media Change: Please insert the disc labeled \'ALT Linux Master CD 3\' in the drive \'/mnt/cdrom/\' and press enter

Get:1 <a href="cdrom://ALT">cdrom://ALT</a> Linux Master CD 3 Mandrake/Master libpwlib-devel 1.2.12-alt1 [394kB]
Fetched 394kB in 25s (15.3kB/s)
Executing RPM (/bin/rpm -Uvh --fancypercent --oldpackage)...

At this point the process hangs until killed by ^C.  Further examination from another terminal gives:

[<a href="mailto:root@sirius" target="_new">root@sirius</a> root]# lsof /var/lib/rpm/Packages 
COMMAND  PID USER   FD   TYPE DEVICE     SIZE NODE NAME
apt-get 3602 root    4uW  REG   3,11 15044608  112 /var/lib/rpm/Packages
rpm     3609 root    3u   REG   3,11 15044608  112 /var/lib/rpm/Packages
[<a href="mailto:root@sirius" target="_new">root@sirius</a> root]# strace -v -p 3602
wait4(3609,  &lt;unfinished ...&gt;
[<a href="mailto:root@sirius" target="_new">root@sirius</a> root]# strace -v -p 3609
fcntl64(3, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0} &lt;unfinished ...&gt;

This shows that rpm is waiting for the database lock, but apt-get did not release it before running rpm, therefore a deadlock happens.

The problem appears only when the packages are fetched from CD-ROM, and more than one CD-ROM disk is used (installation from local files, FTP, or from CD-ROM when only one disk is needed work without this happening).  Repeating the failed apt-get command after killing the hung one with ^C also works (because this time all package files are in the cache).

I have tracked down the problem to a bug in the apt-get code
(apt-0.5.4cnc9/cmdline/apt-get.cc, InstallPackages()).  The problem is that the body of the loop at the end of this function (with the \&quot;Run it\&quot; comment) is executed several times when multiple CD-ROMs are used. Therefore _system-&gt;Lock() at the end of this loop is executed on each pass other than the last, and _system-&gt;UnLock() before  PM-&gt;DoInstall() does not really unlock the database, because the lock count remains greater than zero.

I suggest to move this Lock() call earlier, so that it is called only when UnLock() was called before.  The difference will be that Fetcher.Shutdown() and PM-&gt;GetArchives() will now be called with the lock held, but these operations should work irrespective of the lock state.

The patch is attached (tested with apt-0.5.4cnc9-alt4; -alt6 does not seem to have any changes in the related code - did not test it actually).
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