fix possible infinite loop in intro.cpp thread #2850

Diapolo commented at 11:11 AM on July 23, 2013: none

it was possible to trigger an infinite loop in FreespaceChecker::check() by simply removing the drive letter on Windows (which leads to an infinite loop in the FreespaceChecker thread)
this was caused by not checking if we make progress with parentDir.parent_path()

BitcoinPullTester commented at 11:54 AM on July 23, 2013: none

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in src/qt/intro.cpp:None in e39ad7da9e outdated

  64 | @@ -64,6 +65,14 @@ void FreespaceChecker::check()
  65 |      while(parentDir.has_parent_path() && !fs::exists(parentDir))
  66 |      {
  67 |          parentDir = parentDir.parent_path();
  68 | +        /* Prevent a deadlock by checking if we have something valid in parentDir */
  69 | +        if (!fs::is_regular_file(parentDir) && !fs::is_directory(parentDir) && !fs::is_symlink(parentDir))

laanwj commented at 6:03 AM on July 26, 2013:

Another way to make sure that the loop terminates is to make sure that it makes progress. Ie, continue only as long as parent_path makes the path shorter (it just chops off / or \ delimited parts anyway). These checks seem very arbitrary. A user could enter <existing_directory>/a/b/bitcoin, in which case both a and b don't exist yet so there will be "nothing valid" in parentDir.

btw: This is not a "deadlock", but a garden variety infinite loop. Deadlock is a specific situation in which two threads contend for a lock while they hold another one, which is not the case here.

Diapolo commented at 6:36 AM on July 26, 2013:

I fixed the descriptions, now I need to rework the check.

BitcoinPullTester commented at 7:01 AM on July 26, 2013: none

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fix possible infinite loop in intro.cpp thread

- it was possible to trigger an infinite loop in FreespaceChecker::check() by
  simply removing the drive letter on Windows (which leads to an infinite
  loop in the FreespaceChecker thread)
- this was caused by not checking if we make progress with
  parentDir.parent_path()

5bc6d8e580

Diapolo commented at 7:19 AM on July 26, 2013: none

@laanwj Can you take another look, I'm now checking for progress.

BitcoinPullTester commented at 7:56 AM on July 26, 2013: none

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/5bc6d8e5802500a6ffd737185f30283bc65eba58 for binaries and test log. This test script verifies pulls every time they are updated. It, however, dies sometimes and fails to test properly. If you are waiting on a test, please check timestamps to verify that the test.log is moving at http://jenkins.bluematt.me/pull-tester/current/ Contact BlueMatt on freenode if something looks broken.

laanwj referenced this in commit 6d89611c3a on Aug 1, 2013

laanwj merged this on Aug 1, 2013

laanwj closed this on Aug 1, 2013

IntegralTeam referenced this in commit 0c2fdf4da8 on Jun 4, 2019

DrahtBot locked this on Sep 8, 2021