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  • FreeBSD Errata Notice FreeBSD-EN-24:09.zfs

    From FreeBSD Errata Notices@21:1/5 to All on Thu Apr 25 00:00:07 2024
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    ============================================================================= FreeBSD-EN-24:09.zfs Errata Notice
    The FreeBSD Project

    Topic: High CPU usage by kernel threads related to ZFS

    Category: contrib
    Module: zfs
    Announced: 2024-04-24
    Affects: FreeBSD 13.3
    Corrected: 2024-04-12 13:00:11 UTC (stable/13, 13-STABLE)
    2024-04-24 20:21:10 UTC (releng/13.3, 13.3-RELEASE-p2)

    For general information regarding FreeBSD Errata Notices and Security Advisories, including descriptions of the fields above, security
    branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>.

    I. Background

    ZFS is an advanced and scalable file system originally developed by Sun Microsystems for its Solaris operating system. ZFS was integrated as part of the FreeBSD starting with FreeBSD 7.0, and it has since become a prominent
    and preferred choice for storage management.

    II. Problem Description

    Because ZFS may consume large amounts of RAM to cache various types of filesystem objects, it continuously monitors system RAM available to decide whether to shrink its caches. Some caches are shrunk using a dedicated
    thread, to which work is dispatched asynchronously.

    In some cases, the cache shrinking logic may dispatch excessive amounts of
    work to the "ARC pruning" thread, causing it to continue attempting to shrink caches even after resource shortages are resolved.

    III. Impact

    The bug manifests as a kernel thread, "arc_prune", consuming 100% of a CPU core for indefinite periods, even while the system is otherwise idle. This behavior also impacts workloads running on the system, by reducing available CPU resources and by triggering lock contention in the kernel, in particular with the "vnlru" process whose function is to recycle vnodes (structures representing
    files, whether opened or cached), a mechanism frequently triggered by intensive filesystem workloads.

    IV. Workaround

    No workaround is available. Systems not using ZFS are unaffected.

    V. Solution

    Upgrade your system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. A reboot is required following the upgrade.

    Perform one of the following:

    1) To update your system via a binary patch:

    Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms, or the i386 platform on FreeBSD 13 and earlier, can be updated via
    the freebsd-update(8) utility:

    # freebsd-update fetch
    # freebsd-update install
    # reboot

    2) To update your system via a source code patch:

    The following patches have been verified to apply to the applicable
    FreeBSD release branches.

    a) Download the relevant patch from the location below, and verify the
    detached PGP signature using your PGP utility.

    # fetch https://security.FreeBSD.org/patches/EN-24:09/zfs.patch
    # fetch https://security.FreeBSD.org/patches/EN-24:09/zfs.patch.asc
    # gpg --verify zfs.patch.asc

    b) Apply the patch. Execute the following commands as root:

    # cd /usr/src
    # patch < /path/to/patch

    c) Recompile your kernel as described in <URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
    system.

    VI. Correction details

    This issue is corrected as of the corresponding Git commit hash or Subversion revision number in the following stable and release branches:

    Branch/path Hash Revision
    - ------------------------------------------------------------------------- stable/13/ 330954bdb822 stable/13-n257698 releng/13.3/ 266b3bd3f26d releng/13.3-n257432
    - -------------------------------------------------------------------------

    Run the following command to see which files were modified by a
    particular commit:

    # git show --stat <commit hash>

    Or visit the following URL, replacing NNNNNN with the hash:

    <URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

    To determine the commit count in a working tree (for comparison against
    nNNNNNN in the table above), run:

    # git rev-list --count --first-parent HEAD

    VII. References

    See problem reports <URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=274698> and <URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275594>.

    See also the previous, similar errata notice issued for FreeBSD 14.0: <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-23:18.openzfs.asc>.

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-24:09.zfs.asc> -----BEGIN PGP SIGNATURE-----

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