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xmodmap freezes system with high CPU load for more than one minute

Submitted by nachoparker

Assigned to Xorg Project Team

Link to original bug (#97561)

Description

Created attachment 126163 my modmap

Issuing 'xmodmap mymodmap' causes the x system to freeze for minutes on a high CPU load, or rather, become unresponsive to keyboard or mouse input.

This issue has been reported elsewhere for years, for instance in

I use openbox Openbox 3.6.1 in Arch Linux. Right now I use xserver 1.18.4-1, but this has been happening to me for years ( and the people on the links above ).

Steps to reproduce

  • xmodmap mymodmap

Find mymodmap attached to this bug report.

Some observations:

  • The bigger mymodmap file is ( the more lines ) the longer it takes for the system to come back to responsiveness.

  • I anaylised the Xorg process using perf, and it seems to me that the culprits are ResourceClientBits, GrabMatchesSecond,DeletePassiveGrabFromList and so on, as you can see on this output:

14,63%  Xorg     Xorg                   [.] ResourceClientBits        
11,83%  Xorg     Xorg                   [.] GrabMatchesSecond         
5,17%   Xorg     Xorg                   [.] DeletePassiveGrabFromList 
5,08%   Xorg     Xorg                   [.] AddPassiveGrabToList      
2,44%   Xorg     Xorg                   [.] 0x000000000004fb70       
1,80%   Xorg     [kernel.vmlinux]       [k] do_select               
1,49%   Xorg     [kernel.vmlinux]       [k] unix_poll              
1,33%   Xorg     Xorg                   [.] 0x000000000004fb85    
1,31%   Xorg     Xorg                   [.] 0x000000000004fbd1   
1,21%   Xorg     Xorg                   [.] 0x000000000004fbde  
1,14%   Xorg     Xorg                   [.] 0x000000000004fbc0
  • My system tops at around 23% CPU on all 6 CPUs while irresponsive.

Attachment 126163, "my modmap":
mymodmap

Edited by Alan Coopersmith
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