From c2c8b4787b0882234ba2772ec7513afbf97b563a Mon Sep 17 00:00:00 2001 From: Julian Andres Klode Date: Sun, 29 Jan 2017 13:05:18 +0100 Subject: Add support for dpkg frontend lock The dpkg frontend lock is a lock dpkg tries to acquire except if the frontend already acquires it. This fixes a race condition in the install command where the dpkg lock is not held for a short period of time between different dpkg invocations. For this reason we also define an environment variable DPKG_FRONTEND_LOCKED for dpkg invocations so dpkg knows not to try to acquire the frontend lock because it's held by a parent process. We can set DPKG_FRONTEND_LOCKED only if the frontend lock really is held; that is, if our lock count is greater than 0 - otherwise an apt client not using the LockInner family of functions would run dpkg without the frontend lock set, but with DPKG_FRONTEND_LOCKED set. Such a process has a weaker guarantee: Because dpkg would not lock the frontend lock either, the process is prone to the existing races, and, more importantly, so is a new style process. Closes: #869546 [fixups: fix error messages, add public IsLocked() method, and make {Un,}LockInner return an error on !debSystem] --- apt-private/private-install.cc | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'apt-private') diff --git a/apt-private/private-install.cc b/apt-private/private-install.cc index f90e7097f..4e888a9bd 100644 --- a/apt-private/private-install.cc +++ b/apt-private/private-install.cc @@ -346,7 +346,7 @@ bool InstallPackages(CacheFile &Cache,bool ShwKept,bool Ask, bool Safety) } auto const progress = APT::Progress::PackageManagerProgressFactory(); - _system->UnLock(); + _system->UnLockInner(); pkgPackageManager::OrderResult const Res = PM->DoInstall(progress); delete progress; @@ -355,7 +355,7 @@ bool InstallPackages(CacheFile &Cache,bool ShwKept,bool Ask, bool Safety) if (Res == pkgPackageManager::Completed) break; - _system->Lock(); + _system->LockInner(); // Reload the fetcher object and loop again for media swapping Fetcher.Shutdown(); -- cgit v1.2.3