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docs: fault-injection: document cache-filter feature for failslab

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The failslab fault injection mechanism has an undocumented capability
that provides significant utility in testing and debugging. This feature,
introduced in commit 4c13dd3b48fcb ("failslab: add ability to filter slab
caches"), allows for targeted error injection into specific slab caches.

However, it was inadvertently left undocumented at the time of its
implementation.

Add documentation for the cache-filter feature in the failslab mode
description. Also, providing a practical example demonstrating how to
use cache-filter to inject failures specifically when allocating socket
buffers (skbs).

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240726120930.3231333-1-leitao@debian.org
This commit is contained in:
Breno Leitao 2024-07-26 05:09:30 -07:00 committed by Jonathan Corbet
parent 8663dd38a7
commit 195a56986c
1 changed files with 20 additions and 0 deletions
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20
Documentation/fault-injection/fault-injection.rst
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@ -141,6 +141,14 @@ configuration of fault-injection capabilities.
default is 'Y', setting it to 'N' will also inject failures into
highmem/user allocations (__GFP_HIGHMEM allocations).
- /sys/kernel/debug/failslab/cache-filter
Format: { 'Y' | 'N' }
default is 'N', setting it to 'Y' will only inject failures when
objects are requests from certain caches.
Select the cache by writing '1' to /sys/kernel/slab/<cache>/failslab:
- /sys/kernel/debug/failslab/ignore-gfp-wait:
- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
@ -459,6 +467,18 @@ Application Examples
losetup -d $DEVICE
rm testfile.img
------------------------------------------------------------------------------
- Inject only skbuff allocation failures ::
# mark skbuff_head_cache as faulty
echo 1 > /sys/kernel/slab/skbuff_head_cache/failslab
# Turn on cache filter (off by default)
echo 1 > /sys/kernel/debug/failslab/cache-filter
# Turn on fault injection
echo 1 > /sys/kernel/debug/failslab/times
echo 1 > /sys/kernel/debug/failslab/probability
Tool to run command with failslab or fail_page_alloc
----------------------------------------------------