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![Davidlohr Bueso](/assets/img/avatar_default.png)
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 <dbueso@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Darren Hart <darren@dvhart.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Link: http://lkml.kernel.org/r/1435645562-975-3-git-send-email-dave@stgolabs.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
280 lines
7.8 KiB
Text
280 lines
7.8 KiB
Text
Fault injection capabilities infrastructure
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===========================================
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See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.
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Available fault injection capabilities
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--------------------------------------
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o failslab
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injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
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o fail_page_alloc
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injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
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o fail_futex
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injects futex deadlock and uaddr fault errors.
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o fail_make_request
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injects disk IO errors on devices permitted by setting
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/sys/block/<device>/make-it-fail or
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/sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
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o fail_mmc_request
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injects MMC data errors on devices permitted by setting
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debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
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Configure fault-injection capabilities behavior
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-----------------------------------------------
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o debugfs entries
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fault-inject-debugfs kernel module provides some debugfs entries for runtime
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configuration of fault-injection capabilities.
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- /sys/kernel/debug/fail*/probability:
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likelihood of failure injection, in percent.
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Format: <percent>
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Note that one-failure-per-hundred is a very high error rate
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for some testcases. Consider setting probability=100 and configure
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/sys/kernel/debug/fail*/interval for such testcases.
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- /sys/kernel/debug/fail*/interval:
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specifies the interval between failures, for calls to
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should_fail() that pass all the other tests.
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Note that if you enable this, by setting interval>1, you will
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probably want to set probability=100.
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- /sys/kernel/debug/fail*/times:
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specifies how many times failures may happen at most.
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A value of -1 means "no limit".
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- /sys/kernel/debug/fail*/space:
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specifies an initial resource "budget", decremented by "size"
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on each call to should_fail(,size). Failure injection is
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suppressed until "space" reaches zero.
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- /sys/kernel/debug/fail*/verbose
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Format: { 0 | 1 | 2 }
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specifies the verbosity of the messages when failure is
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injected. '0' means no messages; '1' will print only a single
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log line per failure; '2' will print a call trace too -- useful
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to debug the problems revealed by fault injection.
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- /sys/kernel/debug/fail*/task-filter:
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Format: { 'Y' | 'N' }
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A value of 'N' disables filtering by process (default).
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Any positive value limits failures to only processes indicated by
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/proc/<pid>/make-it-fail==1.
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- /sys/kernel/debug/fail*/require-start:
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- /sys/kernel/debug/fail*/require-end:
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- /sys/kernel/debug/fail*/reject-start:
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- /sys/kernel/debug/fail*/reject-end:
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specifies the range of virtual addresses tested during
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stacktrace walking. Failure is injected only if some caller
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in the walked stacktrace lies within the required range, and
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none lies within the rejected range.
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Default required range is [0,ULONG_MAX) (whole of virtual address space).
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Default rejected range is [0,0).
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- /sys/kernel/debug/fail*/stacktrace-depth:
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specifies the maximum stacktrace depth walked during search
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for a caller within [require-start,require-end) OR
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[reject-start,reject-end).
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- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
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Format: { 'Y' | 'N' }
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default is 'N', setting it to 'Y' won't inject failures into
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highmem/user allocations.
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- /sys/kernel/debug/failslab/ignore-gfp-wait:
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- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
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Format: { 'Y' | 'N' }
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default is 'N', setting it to 'Y' will inject failures
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only into non-sleep allocations (GFP_ATOMIC allocations).
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- /sys/kernel/debug/fail_page_alloc/min-order:
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specifies the minimum page allocation order to be injected
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failures.
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- /sys/kernel/debug/fail_futex/ignore-private:
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Format: { 'Y' | 'N' }
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default is 'N', setting it to 'Y' will disable failure injections
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when dealing with private (address space) futexes.
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o Boot option
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In order to inject faults while debugfs is not available (early boot time),
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use the boot option:
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failslab=
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fail_page_alloc=
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fail_make_request=
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fail_futex=
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mmc_core.fail_request=<interval>,<probability>,<space>,<times>
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How to add new fault injection capability
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-----------------------------------------
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o #include <linux/fault-inject.h>
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o define the fault attributes
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DECLARE_FAULT_INJECTION(name);
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Please see the definition of struct fault_attr in fault-inject.h
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for details.
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o provide a way to configure fault attributes
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- boot option
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If you need to enable the fault injection capability from boot time, you can
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provide boot option to configure it. There is a helper function for it:
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setup_fault_attr(attr, str);
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- debugfs entries
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failslab, fail_page_alloc, and fail_make_request use this way.
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Helper functions:
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fault_create_debugfs_attr(name, parent, attr);
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- module parameters
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If the scope of the fault injection capability is limited to a
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single kernel module, it is better to provide module parameters to
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configure the fault attributes.
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o add a hook to insert failures
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Upon should_fail() returning true, client code should inject a failure.
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should_fail(attr, size);
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Application Examples
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--------------------
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o Inject slab allocation failures into module init/exit code
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#!/bin/bash
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FAILTYPE=failslab
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echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
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echo 10 > /sys/kernel/debug/$FAILTYPE/probability
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echo 100 > /sys/kernel/debug/$FAILTYPE/interval
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echo -1 > /sys/kernel/debug/$FAILTYPE/times
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echo 0 > /sys/kernel/debug/$FAILTYPE/space
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echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
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echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
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faulty_system()
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{
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bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
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}
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if [ $# -eq 0 ]
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then
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echo "Usage: $0 modulename [ modulename ... ]"
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exit 1
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fi
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for m in $*
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do
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echo inserting $m...
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faulty_system modprobe $m
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echo removing $m...
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faulty_system modprobe -r $m
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done
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------------------------------------------------------------------------------
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o Inject page allocation failures only for a specific module
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#!/bin/bash
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FAILTYPE=fail_page_alloc
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module=$1
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if [ -z $module ]
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then
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echo "Usage: $0 <modulename>"
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exit 1
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fi
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modprobe $module
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if [ ! -d /sys/module/$module/sections ]
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then
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echo Module $module is not loaded
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exit 1
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fi
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cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
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cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
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echo N > /sys/kernel/debug/$FAILTYPE/task-filter
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echo 10 > /sys/kernel/debug/$FAILTYPE/probability
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echo 100 > /sys/kernel/debug/$FAILTYPE/interval
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echo -1 > /sys/kernel/debug/$FAILTYPE/times
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echo 0 > /sys/kernel/debug/$FAILTYPE/space
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echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
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echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
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echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
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echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
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trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
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echo "Injecting errors into the module $module... (interrupt to stop)"
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sleep 1000000
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Tool to run command with failslab or fail_page_alloc
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----------------------------------------------------
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In order to make it easier to accomplish the tasks mentioned above, we can use
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tools/testing/fault-injection/failcmd.sh. Please run a command
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"./tools/testing/fault-injection/failcmd.sh --help" for more information and
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see the following examples.
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Examples:
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Run a command "make -C tools/testing/selftests/ run_tests" with injecting slab
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allocation failure.
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# ./tools/testing/fault-injection/failcmd.sh \
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-- make -C tools/testing/selftests/ run_tests
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Same as above except to specify 100 times failures at most instead of one time
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at most by default.
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# ./tools/testing/fault-injection/failcmd.sh --times=100 \
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-- make -C tools/testing/selftests/ run_tests
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Same as above except to inject page allocation failure instead of slab
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allocation failure.
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# env FAILCMD_TYPE=fail_page_alloc \
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./tools/testing/fault-injection/failcmd.sh --times=100 \
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-- make -C tools/testing/selftests/ run_tests
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