Public bug reported: SRU Justification
[Impact] vDSO works with the 5.4.0-1074-azure kernel, but is broken in 5.4.0-1075-azure and newer due to this commit https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-azure/+git/bionic/commit/?h=Ubuntu-azure-5.4-5.4.0-1075.78_18.04.1&id=5c899e1bcda02c755a5327353ed66f0768771644 Please revert the commit 5c899e1bcda02c755a5327353ed66f0768771644. How to verify vDSO is working: "strace date 2>&1 | grep time" should not show the time related syscalls, e.g. clock_gettime() With 5.4.0-1075-azure and newer, I see the time related syscalls. **************************************************************** More info: The buggy commit 5c899e1bcda02c755a5327353ed66f0768771644 was backported from the mainline commit: e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") but due to the differences between the mainline kernel and the 5.4.0-107x-azure kernel, we actually should not simply remove hv_set_clocksource_vdso(). FWIW, the mainline commit is actually buggy and is fixed by this later mainline path: commit 3486d2c9be652a31033363bdd50391b0c8a8fe21 Author: Vitaly Kuznetsov vkuzn...@redhat.com Date: Thu May 13 09:32:46 2021 +0200 clocksource/drivers/hyper-v: Re-enable VDSO_CLOCKMODE_HVCLOCK on X86 Mohammed reports (https://bugzilla.kernel.org/show_bug.cgi?id=213029) the commit e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") broke vDSO on x86. The problem appears to be that VDSO_CLOCKMODE_HVCLOCK is an enum value in 'enum vdso_clock_mode' and '#ifdef VDSO_CLOCKMODE_HVCLOCK' branch evaluates to false (it is not a define). Use a dedicated HAVE_VDSO_CLOCKMODE_HVCLOCK define instead. Fixes: e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") Reported-by: Mohammed Gamal mga...@redhat.com Suggested-by: Thomas Gleixner t...@linutronix.de Signed-off-by: Vitaly Kuznetsov vkuzn...@redhat.com Signed-off-by: Thomas Gleixner t...@linutronix.de Reviewed-by: Michael Kelley mikel...@microsoft.com Link: https://lore.kernel.org/r/20210513073246.1715070-1-vkuzn...@redhat.com PS, Ubunt 20.04’s 5.13.0-1026-azure is not affected. After some discussion it was decided that the revert is the best solution. [Test Case] strace date 2>&1 | grep time also Microsoft tested [Where things could go wrong] vDSO entry point could stop working altogether [Other Info] SF: #00338309 ** Affects: linux-azure (Ubuntu) Importance: Undecided Status: Fix Released ** Affects: linux-azure (Ubuntu Focal) Importance: Medium Assignee: Tim Gardner (timg-tpi) Status: In Progress ** Package changed: linux (Ubuntu) => linux-azure (Ubuntu) ** Changed in: linux-azure (Ubuntu) Status: New => Fix Released ** Also affects: linux-azure (Ubuntu Focal) Importance: Undecided Status: New ** Changed in: linux-azure (Ubuntu Focal) Importance: Undecided => Medium ** Changed in: linux-azure (Ubuntu Focal) Status: New => In Progress ** Changed in: linux-azure (Ubuntu Focal) Assignee: (unassigned) => Tim Gardner (timg-tpi) ** Description changed: SRU Justification [Impact] vDSO works with the 5.4.0-1074-azure kernel, but is broken in 5.4.0-1075-azure and newer due to this commit https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-azure/+git/bionic/commit/?h=Ubuntu-azure-5.4-5.4.0-1075.78_18.04.1&id=5c899e1bcda02c755a5327353ed66f0768771644 Please revert the commit 5c899e1bcda02c755a5327353ed66f0768771644. How to verify vDSO is working: "strace date 2>&1 | grep time" should not show the time related syscalls, e.g. clock_gettime() With 5.4.0-1075-azure and newer, I see the time related syscalls. **************************************************************** More info: The buggy commit 5c899e1bcda02c755a5327353ed66f0768771644 was backported from the mainline commit: e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") but due to the differences between the mainline kernel and the 5.4.0-107x-azure kernel, we actually should not simply remove hv_set_clocksource_vdso(). FWIW, the mainline commit is actually buggy and is fixed by this later mainline path: commit 3486d2c9be652a31033363bdd50391b0c8a8fe21 Author: Vitaly Kuznetsov vkuzn...@redhat.com Date: Thu May 13 09:32:46 2021 +0200 clocksource/drivers/hyper-v: Re-enable VDSO_CLOCKMODE_HVCLOCK on X86 Mohammed reports (https://bugzilla.kernel.org/show_bug.cgi?id=213029) the commit e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") broke vDSO on x86. The problem appears to be that VDSO_CLOCKMODE_HVCLOCK is an enum value in 'enum vdso_clock_mode' and '#ifdef VDSO_CLOCKMODE_HVCLOCK' branch evaluates to false (it is not a define). Use a dedicated HAVE_VDSO_CLOCKMODE_HVCLOCK define instead. Fixes: e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") Reported-by: Mohammed Gamal mga...@redhat.com Suggested-by: Thomas Gleixner t...@linutronix.de Signed-off-by: Vitaly Kuznetsov vkuzn...@redhat.com Signed-off-by: Thomas Gleixner t...@linutronix.de Reviewed-by: Michael Kelley mikel...@microsoft.com Link: https://lore.kernel.org/r/20210513073246.1715070-1-vkuzn...@redhat.com PS, Ubunt 20.04’s 5.13.0-1026-azure is not affected. - After some discussion it was decided that the revert is the solution. + After some discussion it was decided that the revert is the best + solution. [Test Case] strace date 2>&1 | grep time also Microsoft tested [Where things could go wrong] vDSO entry point could stop working altogether [Other Info] SF: #00338309 -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1977753 Title: Azure 5.4: vDSO broken with 5.4.0-1075-azure Status in linux-azure package in Ubuntu: Fix Released Status in linux-azure source package in Focal: In Progress Bug description: SRU Justification [Impact] vDSO works with the 5.4.0-1074-azure kernel, but is broken in 5.4.0-1075-azure and newer due to this commit https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-azure/+git/bionic/commit/?h=Ubuntu-azure-5.4-5.4.0-1075.78_18.04.1&id=5c899e1bcda02c755a5327353ed66f0768771644 Please revert the commit 5c899e1bcda02c755a5327353ed66f0768771644. How to verify vDSO is working: "strace date 2>&1 | grep time" should not show the time related syscalls, e.g. clock_gettime() With 5.4.0-1075-azure and newer, I see the time related syscalls. **************************************************************** More info: The buggy commit 5c899e1bcda02c755a5327353ed66f0768771644 was backported from the mainline commit: e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") but due to the differences between the mainline kernel and the 5.4.0-107x-azure kernel, we actually should not simply remove hv_set_clocksource_vdso(). FWIW, the mainline commit is actually buggy and is fixed by this later mainline path: commit 3486d2c9be652a31033363bdd50391b0c8a8fe21 Author: Vitaly Kuznetsov vkuzn...@redhat.com Date: Thu May 13 09:32:46 2021 +0200 clocksource/drivers/hyper-v: Re-enable VDSO_CLOCKMODE_HVCLOCK on X86 Mohammed reports (https://bugzilla.kernel.org/show_bug.cgi?id=213029) the commit e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") broke vDSO on x86. The problem appears to be that VDSO_CLOCKMODE_HVCLOCK is an enum value in 'enum vdso_clock_mode' and '#ifdef VDSO_CLOCKMODE_HVCLOCK' branch evaluates to false (it is not a define). Use a dedicated HAVE_VDSO_CLOCKMODE_HVCLOCK define instead. Fixes: e4ab4658f1cf ("clocksource/drivers/hyper-v: Handle vDSO differences inline") Reported-by: Mohammed Gamal mga...@redhat.com Suggested-by: Thomas Gleixner t...@linutronix.de Signed-off-by: Vitaly Kuznetsov vkuzn...@redhat.com Signed-off-by: Thomas Gleixner t...@linutronix.de Reviewed-by: Michael Kelley mikel...@microsoft.com Link: https://lore.kernel.org/r/20210513073246.1715070-1-vkuzn...@redhat.com PS, Ubunt 20.04’s 5.13.0-1026-azure is not affected. After some discussion it was decided that the revert is the best solution. [Test Case] strace date 2>&1 | grep time also Microsoft tested [Where things could go wrong] vDSO entry point could stop working altogether [Other Info] SF: #00338309 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-azure/+bug/1977753/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
