Thank you for the comment.
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
MM PGD RSS TOTAL_VM
ffff991572665f00 ffff99158565e000 448808k 2426788k
VMA START END FLAGS FILE
ffff991574e20a18 400000 4de000 8000071 /home/crash/crash
ffff991574e20ab0 4de000 a85000 8000075 /home/crash/crash
ffff991574e20260 a85000 e0f000 8000071 /home/crash/crash
ffff991574e204c0 e0f000 e10000 8100071 /home/crash/crash
ffff991443987980 e10000 e37000 8100073 /home/crash/crash
ffff991574e20720 e37000 1105000 8100073
ffff9914439877b8 21ab000 a178000 8100073
ffff991573b4b5f0 7f4304174000 7f4310000000 8100073
ffff9914d387e098 7f4310000000 7f431006c000 8200073
...
With 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: 51573 TASK: ffff991572868000 CPU: 2 COMMAND: "sshd" <---an expected result
MM PGD RSS TOTAL_VM
ffff991449816900 ffff991442d68000 11168k 18916k
VMA START END FLAGS FILE
ffff991445df8da8 556020069000 556020075000 8000071 /usr/sbin/sshd
ffff991445df8390 556020075000 556020102000 8000075 /usr/sbin/sshd
ffff991445df87b8 556020102000 55602014c000 8000071 /usr/sbin/sshd
ffff991445df8850 55602014c000 556020150000 8100071 /usr/sbin/sshd
ffff99144a5efd10 556020150000 556020151000 8100073 /usr/sbin/sshd
ffff991445df82f8 556020151000 556020155000 8100073
ffff99157750fe40 556020753000 556020838000 8100073
ffff99158602d688 7ff090f6c000 7ff090f73000 8000071 /usr/lib64/libnss_systemd.so.2
...
Another example with an invalid argument:
Without the patch:
crash> vm -M 0xdeadbeef
PID: 51944 TASK: ffff99148c036600 CPU: 2 COMMAND: "crash"
MM PGD RSS TOTAL_VM
ffff9915745e8000 ffff9915728c4000 448684k 2426788k
VMA START END FLAGS FILE
ffff9914c07547b8 400000 4de000 8000071 /home/crash/crash
ffff9914c0754688 4de000 a85000 8000075 /home/crash/crash
ffff9914c0754ed8 a85000 e0f000 8000071 /home/crash/crash
ffff9914c0754c78 e0f000 e10000 8100071 /home/crash/crash
ffff99158554f1c8 e10000 e37000 8100073 /home/crash/crash
ffff9914c07544c0 e37000 1105000 8100073
ffff99158554f098 2b3f000 ab0c000 8100073
ffff9915490871c8 7fde73358000 7fde74321000 8100073
ffff9914c0426260 7fde76b50000 7fde84000000 8100073
...
With the patch:
crash> vm -M 0xdeadbeef
vm: invalid task or pid value: 0xdeadbeef
Hope this helps.
Thanks
Lianbo