Bug 13146

Summary:	memory allocation can sleep
Product:	systemtap	Reporter:	David Smith <dsmith>
Component:	runtime	Assignee:	Unassigned <systemtap>
Status:	RESOLVED FIXED
Severity:	normal
Priority:	P2
Version:	unspecified
Target Milestone:	---
Host:		Target:
Build:		Last reconfirmed:
Bug Depends on:
Bug Blocks:	10994

Description David Smith 2011-09-01 14:35:14 UTC

When the systemtap runtime allocates memory, it uses GFP_KERNEL (possibly with other flags).  GFP_KERNEL includes __GFP_WAIT, which means that the memory allocation could possibly sleep.

Systemtap probe handlers should not sleep.

Comment 1 David Smith 2011-09-01 14:50:44 UTC

Fixed in commit 8e794e9 (which also fixes a couple of places to handle memory allocation failures better).

Regression tested on:

RHEL4:   2.6.9-100.ELsmp (i686)
RHEL5:   2.6.18-274.el5debug (x86_64)
RHEL6:   2.6.32-192.el6.x86_64.debug (x86_64)
f15:     2.6.40.3-0.fc15.i686.debug (i686)
rawhide: 3.0.1-6.fc17.x86_64 (x86_64)

Note that this came up while working on bug #10994.  During some utrace probe handlers, memory allocation is done (typically to allocate space for a pathname).  That is fine, since utrace probe handlers are run in a sleepable context.

However, the new utrace-free task_finder will be implemented via tracepoints, and tracepoint probe handers are not run in a sleepable context.