On 2023/03/17 11:12, lijiang wrote: > Hi, Kazu > Thank you for the comment. > On Fri, Mar 17, 2023 at 9:02 AM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx <mailto:k-hagio-ab@xxxxxxx>> wrote: > > Hi Lianbo, > > On 2023/03/15 18:07, Lianbo Jiang wrote: > > The help/man page of the "vm" command suggests that the "-M" option > > accepts the mm_struct address as a valid argument. However, the "vm > > -M" option always prints the virtual memory data of the current > > task, regardless of its arguments. > > I think that it's the intended behavior, isn't it? > > -M mm if the mm_struct address has been removed from the task_struct > of an exiting task, the virtual memory data cannot be displayed. > However, if the address can be determined from the kernel stack, > it can be entered manually in order to try to resurrect the > virtual memory data of the task. > > They are not the same issues. > > For the live debugging, take the sshd as an example: > > Without the patch: > crash> ps |grep sshd > 1159 1 3 ffff9915858a9980 IN 0.1 15820 9020 sshd > 51573 1159 2 ffff991572868000 IN 0.1 18916 11168 sshd > 51595 51573 2 ffff991575026600 IN 0.0 18784 6892 sshd > crash> vm -M ffff991572868000 > PID: 51727 TASK: ffff9914465cb300 CPU: 0 COMMAND: "crash" <------not a correct result No, I meant that this is correct. Let me explain, (1) The "-M mm" option accepts an *mm_struct* address. (2) The specified mm is enabled only when the mm_struct address has been removedfrom the task_struct, i.e. mm = 0. So we can emulate that situation e.g. with kthreadd (pid=2) like this: crash> vm 1 PID: 1 TASK: ffff900b41599840 CPU: 11 COMMAND: "systemd" MM PGD RSS TOTAL_VM ffff9019ff0e3f00 ffff9019ffc10000 12516k 250328k VMA START END FLAGS FILE ffff900c94de2488 55e2c48d1000 55e2c4a13000 8000875 /usr/lib/systemd/systemd ... crash> vm 2 PID: 2 TASK: ffff900b4159b080 CPU: 2 COMMAND: "kthreadd" MM PGD RSS TOTAL_VM 0 0 0k 0k ^^^ crash> vm 2 -M ffff9019ff0e3f00 <<-- systemd's mm PID: 2 TASK: ffff900b4159b080 CPU: 2 COMMAND: "kthreadd" MM PGD RSS TOTAL_VM 0 0 0k 0k VMA START END FLAGS FILE ffff900c94de2488 55e2c48d1000 55e2c4a13000 8000875 /usr/lib/systemd/systemd I think this is the expected usage of the "-M mm" option. Thanks, Kazu -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/crash-utility Contribution Guidelines: https://github.com/crash-utility/crash/wiki
