April 2021 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

pid start time and new display field in proc pid stat
by Navin P April 3, 2021

April 3, 2021

Hi, As of 5.11 kernel (pid,pid_start_time) is not unique /monotonic even though the underlying counters are . I chose start_boottime because i wanted the counter to increase during suspend as well. 1. Is there any case where task->start_boottime or ktime_get_boottime_ns doesn't become monotonic i.e increasing ? 2. If start_boottime is not monotonic which counter to use ? 3. If i create a new field in task_struct , then i can use a atomic_add_return(1,&v) to fill in the task->new_field. Will this also work ? By doing this <pid,pid_start_time> becomes unique. In linux/fs/proc/array.c at line 566 we have /* apply timens offset for boottime and convert nsec -> ticks */ start_time = nsec_to_clock_t(timens_add_boottime_ns(task->start_boottime)); task->start_boottime is a monotonic increasing counter fetched from ktime_get_boottime_ns in fork.c nsec_to_clock_t contains div_u64 due to which we loose some lower bits/digits on divison and is not unique unless the divisor is 1. if CONFIG_HZ = 250 and nsec_to_clock_t x=4000001 , then #if (NSEC_PER_SEC % USER_HZ) == 0 return div_u64(x, NSEC_PER_SEC / USER_HZ); becomes div_u64(x, 4000000) then return value is 1 when x=4000002, return value is 1 until x=8000000 which returns 2. The value shown in /proc/[pid]/stat is actually the truncated value. Hence i'm planning to display a counter at the end of /proc/[pid]/stat as the 53rd field. I've prepared a patch as inlined. >From a2c6b5d6435394f015d38700008ff74f16dfa5fd Mon Sep 17 00:00:00 2001 From: Navin P <navinp0304(a)gmail.com> Date: Thu, 25 Mar 2021 15:27:30 +0530 Subject: [PATCH] Display task->start_boottime as 53rd field in /proc/[pid]/stat. The 22nd field start_time currently shown in /proc/[pid]/stat as start_time is truncated by division.Hence it is not unique . Signed-off-by: Navin P <navinp0304(a)gmail.com> --- Documentation/filesystems/proc.rst | 1 + fs/proc/array.c | 1 + 2 files changed, 2 insertions(+) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 48fbfc336ebf..3b7a1543b2c0 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -381,6 +381,7 @@ It's slow but very precise. env_end address below which program environment is placed exit_code the thread's exit_code in the form reported by the waitpid system call + start_boottime the process start time in nanoseconds since boot ============= =============================================================== The /proc/PID/maps file contains the currently mapped memory regions and diff --git a/fs/proc/array.c b/fs/proc/array.c index bb87e4d89cd8..74389aaefa9c 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -645,6 +645,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, else seq_puts(m, " 0"); + seq_put_decimal_ull(m, " ", task->start_boottime); seq_putc(m, '\n'); if (mm) mmput(mm); -- 2.25.1

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Unable to boot to kernel built from stable 5.11.y
by Andrew Adamson April 2, 2021

April 2, 2021

Hi Everyone, I tried to build the kernel myself for the first a few days ago. While the build was successful, I am unable to boot to it. After grub I get a blinking cursor for 15 to 30 minutes, and then a message that says "Please reboot and select proper boot device." Since ubuntu ships with a 5.4 kernel, I copied the config from /boot and used make olddefconfig. I also checked the menu entries in grub and my 5.11.y entry looks identical to my 5.4.y entry. This feels like a config issue with how ubuntu configures the boot process, but I am not sure how to investigate. I checked the ubuntu wiki for advice on kernel building, and noticed they recommend using make deb-pkg instead of make all. I cannot get that make recipe to work, it throws errors from dpkg-source that I'm not sure how to resolve """ dpkg-source: error: unrepresentable changes to source dpkg-buildpackage: error: dpkg-source -i.git -b . subprocess returned exit status 1 """ Does anyone have any recommendations? Thanks in advance -Andrew

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memory order seq cst for atomics
by Navin P April 2, 2021

April 2, 2021

Hi, C11 and c++11 have memory order like memory_order_seq_cst .What is the equivalent in Linux kernel ? atomic64_inc(&var) ; __SMP_mb(); Regards, Navin

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Status of a kernel.org hosted project, mmsd?
by Chris Talbot April 1, 2021

April 1, 2021

Hello, I am reaching out here in the hopes of finding out the status of a kernel.org hosted project, mmsd. Bottom line, I think it is abandoned. I think this based on on the fact that despite attempting to contact the maintainers several times in the past few months over several forms of communication, I never got a reply. Additionally, it seems to have not been worked on in quite some time. I am trying to find out how I can submit patches for it, and if it makes sense to find a new maintainer for it. Upstream is here: https://git.kernel.org/pub/scm/network/ofono/mmsd.git I have attempted to contact the ofono maintainers via IRC in December 2020, January 2021, and February 2021 in regards to submitting patches. I have yet to recieve a reply. I also tried to submit patches for mmsd on the Ofono Mailing List starting in February of 2021: https://lists.ofono.org/hyperkitty/list/ofono@ofono.org/thread/HFGZCER3I6G5… https://lists.ofono.org/hyperkitty/list/ofono@ofono.org/thread/CVOWCDC7H4G4… https://lists.ofono.org/hyperkitty/list/ofono@ofono.org/thread/C47Q5UY2NVHQ… None of my emails got a reply. At the advice of some other devs, I have additionally tried emailling the Linux-netdev group mailing list, the authors listed on mmsd, and the folks who have contributed in the past, but that also did not recieve a reply. If you are curious to see the status of my work, it is here: https://source.puri.sm/kop316/mmsd/ Thank you for your time! Respectfully, Chris Talbot

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Re: Missing RUST_EXAMPLE option in linux-next
by Manas April 1, 2021

April 1, 2021

Hi, I am working on a device driver in rust in linux-next as an academic project. I used the following command to create .config: $ make LLVM=1 menuconfig But, sometimes the RUST_EXAMPLE option is not visible in menuconfig (under /Device Drivers/Character devices/). It seemingly happens at random that this option disappears, despite having a working rust nightly environment (and other dependencies). Can someone point me to why is this happening? Also, if this is not the right place for this query, please let me know. Thank you -- Manas CSAM Undergraduate | 2022 IIIT-Delhi, India

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