July 2020 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Regarding Linux kernel SMP and task switching CPU
by William Tambe July 13, 2020

July 13, 2020

When a task is moved from one CPU to another, are there platform specific functions that are called to detect change ?

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RE: Are kernel trees the same as a branch in terms of git?
by cristian andres vargas gonzalez July 13, 2020

July 13, 2020

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Are kernel trees the same as a branch in terms of git?
by CRISTIAN ANDRES VARGAS GONZALEZ July 12, 2020

July 12, 2020

Hi guys, there is something I want to know, in the Linux kernel mailing list some developers refer to URLs like these tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master. I doubt that in my learning about git I have not seen any source code called tree so I want to know if a kernel tree is a branch? very thanks :)

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Turn private hugetlb mapping into VM_SHARED
by heep July 12, 2020

July 12, 2020

Hello, list, I am working on a tool to introspect live memory of KVM machines, and mmapping its memory, instead of calling process_vm_readv on every read, would increase its performance significantly. Understandably, almost all virtual machine monitors (like QEMU) create private mappings for the memory. So, trying to understand the memory managment subsystem I am hoping to write a kernel module to do the remappings, and conversion from private, to shared mappings. My current focus is on hugetlb pages. At first, I remapped the pages using remap_pfn_range, but there is a memory safety risk when the VM shuts off, and that memory gets used elsewhere. Now, I am trying to turn the underlying mapping into a shared one, so that the kernel can keep track of the memory used. What would be the best way to do so? I noticed there is resv_map that stores represented mappings, and while on private mappings it's on vma, on the shared ones - it is in the inode, but making the inode point to the VMAs map leads to a bus error in userspace. I must be missing some key pieces. Does anyone know how to best achieve what I am trying to? Or is it something fundamentally wrong to do? Many thanks, Auri B.

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Why are there "<IRQ>" and "</IRQ>" in the call trace section? What does them imply?
by 孙世龙 sunshilong July 12, 2020

July 12, 2020

Hi, list As the subject, here is the related log: [72873.713472] Call Trace: [72873.713473] <IRQ> [72873.713474] switch_mm_irqs_off+0x31b/0x4e0 [72873.713475] xnarch_switch_to+0x2f/0x80 [72873.713476] ___xnsched_run.part.74+0x154/0x480 [72873.713476] ___xnsched_run+0x35/0x50 [72873.713477] xnintr_irq_handler+0x346/0x4c0 [72873.713478] ? xnintr_core_clock_handler+0x1b6/0x360 [72873.713479] dispatch_irq_head+0x8e/0x110 [72873.713479] ? xnintr_irq_handler+0x5/0x4c0 [72873.713481] ? dispatch_irq_head+0x8e/0x110 [72873.713482] __ipipe_dispatch_irq+0xd9/0x1c0 [72873.713483] __ipipe_handle_irq+0x86/0x1e0 [72873.713483] common_interrupt+0xf/0x2c [72873.713484] </IRQ> Maybe, the later one(i.e. </IRQ>) implies there was an interrupt request and the common_interuppt() function handler it. Am I right? But what about the former one(i.e. <IRQ>)? Thank you for your attention to this matter.

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What are the major differences between soft lockup and hard lockup which are both detected by watchdog?
by 孙世龙 sunshilong July 11, 2020

July 11, 2020

What are the major differences between soft lockup and hard lockup which are both detected by watchdog? Here are some example logs: 1. Watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [cantest:1669] 2. NMI watchdog: Watchdog detected hard LOCKUP on CPU 0 Best regards.

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What methods or tools could be used to investigate the causes of hard or soft lockup?
by 孙世龙 sunshilong July 11, 2020

July 11, 2020

Hi, list I have frequently faced sort lockups and hard lockups. Here are some example logs: 1. Watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [cantest:1669] 2. NMI watchdog: Watchdog detected hard LOCKUP on CPU 0 What methods or tools could be used to investigate the causes of hard or soft lockups? I have been stuck with such problems for a long time. I would be grateful if somebody shed some light on this issue. Any advice on how to proceed? Thank you for your attention to this matter. Best regards.

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Re: new TODO list item
by Suraj Upadhyay July 10, 2020

July 10, 2020

On Tue, Apr 21, 2020 at 04:26:16AM -0700, Christoph Hellwig wrote: > On Tue, Apr 21, 2020 at 01:53:25PM +0530, Suraj Upadhyay wrote: > > On Tue, Apr 21, 2020 at 10:12:57AM +0200, Christoph Hellwig wrote: > > > Hi Janitors, > > > > > > if someone feels like helping with a fairly trivial legacy API, the > > > wrappers in include/linux/pci-dma-compat.h should go away. This is > > > mostly trivially scriptable, except for dma_alloc_coherent, where > > > the GFP_ATOMIC passed by pci_alloc_consisteny should usually be replaced > > > with GFP_KERNEL when not calling from an atomic context. > > > > Hii Christoph, > > This is my first time posting to kernel-janitors. I would be glad to > > help with this task but suggest me if I should get started with > > something else. > > Sure, feel free to get started. A coccinelle script to do the grunt > work might be useful, though. Hii Christoph, I nearly forgot about this, and now I would like to complete this task. However, even after two months I am still a newbie and there are a few questions that I would like to ask : 1. Multiple files will be affected by this change, who do you think I should send my patches to ?? 2. Should I send my patches as a patchset of multiple small patches chaging a particular API for e.g. sending all patches that change pci_map_single() to dma_map_single() in one file in the same patchset ?? 3. I literally have little idea on how to change the comments and docs which refer to these APIs. 4. And what if a maintainer likes the previous APIs for simplicity and rejects the patches that try to change them ?? Thanks, Suraj Upadhyay. CCing Kernelnewbies(a)kernelnewbies.org

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how to debug problem with "failing unmounting"
by Tomek The Messenger July 9, 2020

July 9, 2020

Hi On the soc on which I work there is issue with unmouting some partitions/directories during /sbin/reboot, here is some example: [ OK ] Stopped target Local File System. Unmouting Temporary Directory (/tmp)... Unmouting /run/user/0... ... [ FAILED ] Failed unmouting Temporary Directory (/tmp). [ FAILED ] Failed unmouting /run/user/0. .... Unfortunately like it is typical in kernel information about why unmouting failed doesn't appear. So seems like searching in darkness what is going on. Is any way how to search in darkness? Firstly I should make sure /tmp or /run/user/0 is really a partition and was mount at linux startup. Then maybe I should check access rights if it is rwx. What else can be tried here?

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What are the most frequently used methods for system level-tracing?
by 孙世龙 sunshilong July 9, 2020

July 9, 2020

Hi, list What are the most frequently used methods for system level-tracing? I would appreciate it if you could give me some related documents to go through. Thank you for your attention to this matter. Best regards.

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