Commit Graph

1 Commits

Author SHA1 Message Date
Philipp Rudo
90da030e61 add generic cycle detection
Resolves: bz2069200
Upstream: github.com/makedumpfile/makedumpfile.git
Conflicts: None

commit feae3d1754d2b0788ce1f18b0cd4b40098ff52ff
Author: Philipp Rudo <prudo@redhat.com>
Date:   Mon Mar 14 17:04:29 2022 +0100

    [PATCH v2 1/3] add generic cycle detection

    In order to work makedumpfile needs to interpret data read from the
    dump. This can cause problems as the data from the dump cannot be
    trusted (otherwise the kernel wouldn't have panicked in the first
    place). This also means that every loop which stop condition depend on
    data read from the dump has a chance to loop forever. Thus add a generic
    cycle detection mechanism that allows to detect and handle such
    situations appropriately.

    For cycle detection use Brent's algorithm [1] as it has constant memory
    usage. With this it can also be used in the kdump kernel without the
    danger that it runs oom when iterating large data structures.
    Furthermore it only depends on some pointer arithmetic. Thus the
    performance impact (as long as no cycle was detected) should be
    comparatively small.

    [1] https://en.wikipedia.org/wiki/Cycle_detection#Brent's_algorithm

    Suggested-by: Dave Wysochanski <dwysocha@redhat.com>
    Signed-off-by: Philipp Rudo <prudo@redhat.com>
    Reviewed-and-tested-by: Dave Wysochanski <dwysocha@redhat.com>

Signed-off-by: Philipp Rudo <prudo@redhat.com>
2022-03-28 18:38:30 +02:00