path: root/Documentation/fault-injection
diff options
authorDavidlohr Bueso <>2015-06-29 23:26:02 -0700
committerThomas Gleixner <>2015-07-20 11:45:45 +0200
commitab51fbab39d864f3223e44a2600fd951df261f0b (patch)
treecd8106193d0d15b9690a8e80ceec85d202f8e1cb /Documentation/fault-injection
parent767f509ca11269c2bcd92e3972a93096f2173ac0 (diff)
futex: Fault/error injection capabilities
Although futexes are well known for being a royal pita, we really have very little debugging capabilities - except for relying on tglx's eye half the time. By simply making use of the existing fault-injection machinery, we can improve this situation, allowing generating artificial uaddress faults and deadlock scenarios. Of course, when this is disabled in production systems, the overhead for failure checks is practically zero -- so this is very cheap at the same time. Future work would be nice to now enhance trinity to make use of this. There is a special tunable 'ignore-private', which can filter out private futexes. Given the tsk->make_it_fail filter and this option, pi futexes can be narrowed down pretty closely. Signed-off-by: Davidlohr Bueso <> Cc: Peter Zijlstra <> Cc: Darren Hart <> Cc: Davidlohr Bueso <> Link: Signed-off-by: Thomas Gleixner <>
Diffstat (limited to 'Documentation/fault-injection')
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt
index 4cf1a2a6bd72..415484f3d59a 100644
--- a/Documentation/fault-injection/fault-injection.txt
+++ b/Documentation/fault-injection/fault-injection.txt
@@ -15,6 +15,10 @@ o fail_page_alloc
injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
+o fail_futex
+ injects futex deadlock and uaddr fault errors.
o fail_make_request
injects disk IO errors on devices permitted by setting
@@ -113,6 +117,12 @@ configuration of fault-injection capabilities.
specifies the minimum page allocation order to be injected
+- /sys/kernel/debug/fail_futex/ignore-private:
+ Format: { 'Y' | 'N' }
+ default is 'N', setting it to 'Y' will disable failure injections
+ when dealing with private (address space) futexes.
o Boot option
In order to inject faults while debugfs is not available (early boot time),
@@ -121,6 +131,7 @@ use the boot option:
+ fail_futex=
How to add new fault injection capability