Bug 243311

Summary: printk in atomic can schedule
Product: Red Hat Enterprise MRG Reporter: Steven Rostedt <srostedt>
Component: realtime-kernelAssignee: Steven Rostedt <srostedt>
Status: CLOSED CURRENTRELEASE QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: 1.0CC: sripathi
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Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: 2.6.21-35.el5rt Doc Type: Bug Fix
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Last Closed: 2007-07-26 14:36:10 UTC Type: ---
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Description Steven Rostedt 2007-06-08 14:59:32 UTC 
Description of problem:
printk calls consol functions that write to the appropriate devices.
But in the PREEMPT_RT kernel, some of these console functions grab
spin locks that are converted to mutexes.  This means that calling
printk in an atomic operation or from interrupt contex can schedule
and cause undefined results.

Version-Release number of selected component (if applicable):


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Additional info:
I need to write a patch that will add an ATOMIC_SAFE flag to the console
drivers. This will be checked if printk is called from an atomic
operation. If the console is not safe, then printk will skip that
console.  Current consoles that should be atomic safe, is the VGA
console as well as early_printk console.
Comment 1 Clark Williams 2007-07-26 14:36:10 UTC 
Patch applied