[LU-10444] l_getidentity keeps remount /sys/kernel/debug and reverting permissions.

Related — Fri, 9 Feb 2018 21:57:43 +0000

We change the permissions of /sys/kernel/debug to 755. But it kept revering to 700.

Using systemtap script

#!/usr/bin/env stap

probe kernel.function("debug_mount") {
 printf("mounting ")
 printf("pid %i %s %s %s \n", pid(),execname(), cmdline_str(), caller())
 print_backtrace()
}

probe kernel.function("debugfs_remount") {
 printf("remounting ")
 printf("pid %i %s %s %s \n", pid(),execname(), cmdline_str(), caller())
 print_backtrace()
}

I tracked this down to l_getidentity. Specificly cfs_get_param_paths keeps remounting /sys/kernel/debug.

# mount -o remount,mode=755 /sys/kernel/debug
debugfs on /sys/kernel/debug type debugfs (rw,relatime,mode=755)

Here is the output from the systemtap

nbp1-mds ~ # stap -v debug_mount.stp 
Pass 1: parsed user script and 468 library scripts using 122940virt/39548res/3192shr/36448data kb, in 340usr/20sys/351real ms.
Pass 2: analyzed script: 2 probes, 22 functions, 5 embeds, 0 globals using 161632virt/79356res/4388shr/75140data kb, in 580usr/80sys/665real ms.
Pass 3: translated to C into "/tmp/stapYTzkIl/stap_6d34b35e04d11e38ae0c8b364ac253de_10487_src.c" using 162160virt/80148res/4692shr/75668data kb, in 340usr/10sys/353real ms.
Pass 4: compiled C into "stap_6d34b35e04d11e38ae0c8b364ac253de_10487.ko" in 5660usr/860sys/5857real ms.
Pass 5: starting run.
mounting pid 9739 l_getidentity "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" mount_fs 0xffffffff811fec69 
 0xffffffff81289120 : debug_mount+0x0/0x20 [kernel]
 0xffffffff811fec69 : mount_fs+0x39/0x1b0 [kernel]
 0xffffffff8121b5c7 : vfs_kern_mount+0x67/0x110 [kernel]
 0xffffffff8121dad3 : do_mount+0x233/0xaf0 [kernel]
 0xffffffff8121e716 : SyS_mount+0x96/0xf0 [kernel]
 0xffffffff81695b89 : system_call_fastpath+0x16/0x1b [kernel]
remounting pid 9739 l_getidentity "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" do_remount_sb 0xffffffff811fe7c2 
 0xffffffff81289330 : debugfs_remount+0x0/0x50 [kernel]
 0xffffffff811fe7c2 : do_remount_sb+0x72/0x200 [kernel]
 0xffffffff811feb07 : mount_single+0x57/0xc0 [kernel]
 0xffffffff81289138 : debug_mount+0x18/0x20 [kernel]
 0xffffffff811fec69 : mount_fs+0x39/0x1b0 [kernel]
 0xffffffff8121b5c7 : vfs_kern_mount+0x67/0x110 [kernel]
 0xffffffff8121dad3 : do_mount+0x233/0xaf0 [kernel]
 0xffffffff8121e716 : SyS_mount+0x96/0xf0 [kernel]
 0xffffffff81695b89 : system_call_fastpath+0x16/0x1b [kernel]
mounting pid 9779 l_getidentity "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" mount_fs 0xffffffff811fec69 
 0xffffffff81289120 : debug_mount+0x0/0x20 [kernel]
 0xffffffff811fec69 : mount_fs+0x39/0x1b0 [kernel]
 0xffffffff8121b5c7 : vfs_kern_mount+0x67/0x110 [kernel]
 0xffffffff8121dad3 : do_mount+0x233/0xaf0 [kernel]
 0xffffffff8121e716 : SyS_mount+0x96/0xf0 [kernel]
 0xffffffff81695b89 : system_call_fastpath+0x16/0x1b [kernel]
remounting pid 9779 l_getidentity "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" do_remount_sb 0xffffffff811fe7c2 
 0xffffffff81289330 : debugfs_remount+0x0/0x50 [kernel]
 0xffffffff811fe7c2 : do_remount_sb+0x72/0x200 [kernel]
 0xffffffff811feb07 : mount_single+0x57/0xc0 [kernel]
 0xffffffff81289138 : debug_mount+0x18/0x20 [kernel]
 0xffffffff811fec69 : mount_fs+0x39/0x1b0 [kernel]
 0xffffffff8121b5c7 : vfs_kern_mount+0x67/0x110 [kernel]
 0xffffffff8121dad3 : do_mount+0x233/0xaf0 [kernel]
 0xffffffff8121e716 : SyS_mount+0x96/0xf0 [kernel]
 0xffffffff81695b89 : system_call_fastpath+0x16/0x1b [kernel]

Whamcloud Community JIRA

[LU-10444] l_getidentity keeps remount /sys/kernel/debug and reverting permissions.