linux-stable.git/Documentation/dev-tools, branch v5.15.208

kfence: allow use of a deferrable timer

2025-03-13T11:50:49+00:00

[ Upstream commit 737b6a10ac19e41877aa1911bf6b361a72a88ad9 ]

Allow the use of a deferrable timer, which does not force CPU wake-ups
when the system is idle.  A consequence is that the sample interval
becomes very unpredictable, to the point that it is not guaranteed that
the KFENCE KUnit test still passes.

Nevertheless, on power-constrained systems this may be preferable, so
let's give the user the option should they accept the above trade-off.

Link: https://lkml.kernel.org/r/20220308141415.3168078-1-elver@google.com
Signed-off-by: Marco Elver 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Stable-dep-of: e64f81946adf ("kfence: skip __GFP_THISNODE allocations on NUMA systems")
Signed-off-by: Sasha Levin

docs/scripts/gdb: add necessary make scripts_gdb step

2023-03-10T08:39:53+00:00

[ Upstream commit 6b219431037bf98c9efd49716aea9b68440477a3 ]

In order to debug the kernel successfully with gdb you need to run
'make scripts_gdb' nowadays.

This was changed with the following commit:

Commit 67274c083438340ad16c ("scripts/gdb: delay generation of gdb
constants.py")

In order to have a complete guide for beginners this remark
should be added to the offial documentation.

Signed-off-by: Jakob Koschel 
Link: https://lore.kernel.org/r/20230112-documentation-gdb-v2-1-292785c43dc9@gmail.com
Signed-off-by: Jonathan Corbet 
Signed-off-by: Sasha Levin

kfence: default to dynamic branch instead of static keys mode

2021-11-12T14:05:49+00:00

commit 4f612ed3f748962cbef1316ff3d323e2b9055b6e upstream.

We have observed that on very large machines with newer CPUs, the static
key/branch switching delay is on the order of milliseconds.  This is due
to the required broadcast IPIs, which simply does not scale well to
hundreds of CPUs (cores).  If done too frequently, this can adversely
affect tail latencies of various workloads.

One workaround is to increase the sample interval to several seconds,
while decreasing sampled allocation coverage, but the problem still
exists and could still increase tail latencies.

As already noted in the Kconfig help text, there are trade-offs: at
lower sample intervals the dynamic branch results in better performance;
however, at very large sample intervals, the static keys mode can result
in better performance -- careful benchmarking is recommended.

Our initial benchmarking showed that with large enough sample intervals
and workloads stressing the allocator, the static keys mode was slightly
better.  Evaluating and observing the possible system-wide side-effects
of the static-key-switching induced broadcast IPIs, however, was a blind
spot (in particular on large machines with 100s of cores).

Therefore, a major downside of the static keys mode is, unfortunately,
that it is hard to predict performance on new system architectures and
topologies, but also making conclusions about performance of new
workloads based on a limited set of benchmarks.

Most distributions will simply select the defaults, while targeting a
large variety of different workloads and system architectures.  As such,
the better default is CONFIG_KFENCE_STATIC_KEYS=n, and re-enabling it is
only recommended after careful evaluation.

For reference, on x86-64 the condition in kfence_alloc() generates
exactly
2 instructions in the kmem_cache_alloc() fast-path:

 | ...
 | cmpl   $0x0,0x1a8021c(%rip)  # ffffffff82d560d0 
 | je     ffffffff812d6003      
 | ...

which, given kfence_allocation_gate is infrequently modified, should be
well predicted by most CPUs.

Link: https://lkml.kernel.org/r/20211019102524.2807208-2-elver@google.com
Signed-off-by: Marco Elver 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Jann Horn 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

Merge branch 'akpm' (patches from Andrew)

2021-09-08T19:55:35+00:00

Merge more updates from Andrew Morton:
 "147 patches, based on 7d2a07b769330c34b4deabeed939325c77a7ec2f.

  Subsystems affected by this patch series: mm (memory-hotplug, rmap,
  ioremap, highmem, cleanups, secretmem, kfence, damon, and vmscan),
  alpha, percpu, procfs, misc, core-kernel, MAINTAINERS, lib,
  checkpatch, epoll, init, nilfs2, coredump, fork, pids, criu, kconfig,
  selftests, ipc, and scripts"

* emailed patches from Andrew Morton : (94 commits)
  scripts: check_extable: fix typo in user error message
  mm/workingset: correct kernel-doc notations
  ipc: replace costly bailout check in sysvipc_find_ipc()
  selftests/memfd: remove unused variable
  Kconfig.debug: drop selecting non-existing HARDLOCKUP_DETECTOR_ARCH
  configs: remove the obsolete CONFIG_INPUT_POLLDEV
  prctl: allow to setup brk for et_dyn executables
  pid: cleanup the stale comment mentioning pidmap_init().
  kernel/fork.c: unexport get_{mm,task}_exe_file
  coredump: fix memleak in dump_vma_snapshot()
  fs/coredump.c: log if a core dump is aborted due to changed file permissions
  nilfs2: use refcount_dec_and_lock() to fix potential UAF
  nilfs2: fix memory leak in nilfs_sysfs_delete_snapshot_group
  nilfs2: fix memory leak in nilfs_sysfs_create_snapshot_group
  nilfs2: fix memory leak in nilfs_sysfs_delete_##name##_group
  nilfs2: fix memory leak in nilfs_sysfs_create_##name##_group
  nilfs2: fix NULL pointer in nilfs_##name##_attr_release
  nilfs2: fix memory leak in nilfs_sysfs_create_device_group
  trap: cleanup trap_init()
  init: move usermodehelper_enable() to populate_rootfs()
  ...

kfence: show cpu and timestamp in alloc/free info

2021-09-08T18:50:24+00:00

Record cpu and timestamp on allocations and frees, and show them in
reports.  Upon an error, this can help correlate earlier messages in the
kernel log via allocation and free timestamps.

Link: https://lkml.kernel.org/r/20210714175312.2947941-1-elver@google.com
Suggested-by: Joern Engel 
Signed-off-by: Marco Elver 
Acked-by: Alexander Potapenko 
Acked-by: Joern Engel 
Cc: Yuanyuan Zhong 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'akpm' (patches from Andrew)

2021-09-03T17:08:28+00:00

Merge misc updates from Andrew Morton:
 "173 patches.

  Subsystems affected by this series: ia64, ocfs2, block, and mm (debug,
  pagecache, gup, swap, shmem, memcg, selftests, pagemap, mremap,
  bootmem, sparsemem, vmalloc, kasan, pagealloc, memory-failure,
  hugetlb, userfaultfd, vmscan, compaction, mempolicy, memblock,
  oom-kill, migration, ksm, percpu, vmstat, and madvise)"

* emailed patches from Andrew Morton : (173 commits)
  mm/madvise: add MADV_WILLNEED to process_madvise()
  mm/vmstat: remove unneeded return value
  mm/vmstat: simplify the array size calculation
  mm/vmstat: correct some wrong comments
  mm/percpu,c: remove obsolete comments of pcpu_chunk_populated()
  selftests: vm: add COW time test for KSM pages
  selftests: vm: add KSM merging time test
  mm: KSM: fix data type
  selftests: vm: add KSM merging across nodes test
  selftests: vm: add KSM zero page merging test
  selftests: vm: add KSM unmerge test
  selftests: vm: add KSM merge test
  mm/migrate: correct kernel-doc notation
  mm: wire up syscall process_mrelease
  mm: introduce process_mrelease system call
  memblock: make memblock_find_in_range method private
  mm/mempolicy.c: use in_task() in mempolicy_slab_node()
  mm/mempolicy: unify the create() func for bind/interleave/prefer-many policies
  mm/mempolicy: advertise new MPOL_PREFERRED_MANY
  mm/hugetlb: add support for mempolicy MPOL_PREFERRED_MANY
  ...

mm/kasan: move kasan.fault to mm/kasan/report.c

2021-09-03T16:58:14+00:00

Move the boot parameter 'kasan.fault' from hw_tags.c to report.c, so it
can support all KASAN modes - generic, and both tag-based.

Link: https://lkml.kernel.org/r/20210713010536.3161822-1-woodylin@google.com
Signed-off-by: Woody Lin 
Reviewed-by: Marco Elver 
Reviewed-by: Andrey Konovalov 
Cc: Andrey Ryabinin 
Cc: Dmitry Vyukov 
Cc: Alexander Potapenko 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge tag 'locking-debug-2021-09-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-09-02T20:00:15+00:00

Pull memory model updates from Ingo Molnar:
 "LKMM updates:

   - Update documentation and code example

  KCSAN updates:

   - Introduce CONFIG_KCSAN_STRICT (which RCU uses)

   - Optimize use of get_ctx() by kcsan_found_watchpoint()

   - Rework atomic.h into permissive.h

   - Add the ability to ignore writes that change only one bit of a
     given data-racy variable.

   - Improve comments"

* tag 'locking-debug-2021-09-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tools/memory-model: Document data_race(READ_ONCE())
  tools/memory-model: Heuristics using data_race() must handle all values
  tools/memory-model: Add example for heuristic lockless reads
  tools/memory-model: Make read_foo_diagnostic() more clearly diagnostic
  kcsan: Make strict mode imply interruptible watchers
  kcsan: permissive: Ignore data-racy 1-bit value changes
  kcsan: Print if strict or non-strict during init
  kcsan: Rework atomic.h into permissive.h
  kcsan: Reduce get_ctx() uses in kcsan_found_watchpoint()
  kcsan: Introduce CONFIG_KCSAN_STRICT
  kcsan: Remove CONFIG_KCSAN_DEBUG
  kcsan: Improve some Kconfig comments

kunit: tool: make --raw_output support only showing kunit output

2021-08-13T19:32:01+00:00

--raw_output is nice, but it would be nicer if could show only output
after KUnit tests have started.

So change the flag to allow specifying a string ('kunit').
Make it so `--raw_output` alone will default to `--raw_output=all` and
have the same original behavior.

Drop the small kunit_parser.raw_output() function since it feels wrong
to put it in "kunit_parser.py" when the point of it is to not parse
anything.

E.g.

$ ./tools/testing/kunit/kunit.py run --raw_output=kunit
...
[15:24:07] Starting KUnit Kernel ...
TAP version 14
1..1
    # Subtest: example
    1..3
    # example_simple_test: initializing
    ok 1 - example_simple_test
    # example_skip_test: initializing
    # example_skip_test: You should not see a line below.
    ok 2 - example_skip_test # SKIP this test should be skipped
    # example_mark_skipped_test: initializing
    # example_mark_skipped_test: You should see a line below.
    # example_mark_skipped_test: You should see this line.
    ok 3 - example_mark_skipped_test # SKIP this test should be skipped
ok 1 - example
[15:24:10] Elapsed time: 6.487s total, 0.001s configuring, 3.510s building, 0.000s running

Signed-off-by: Daniel Latypov 
Reviewed-by: David Gow 
Signed-off-by: Shuah Khan

kunit: tool: add --kernel_args to allow setting module params

2021-08-13T19:28:47+00:00

kunit.py currently does not make it possible for users to specify module
parameters (/kernel arguments more generally) unless one directly tweaks
the kunit.py code itself.

This hasn't mattered much so far, but this would make it easier to port
existing tests that expose module parameters over to KUnit and/or let
current KUnit tests take advantage of them.

Tested using an kunit internal parameter:
$ ./tools/testing/kunit/kunit.py run --kunitconfig=lib/kunit \
    --kernel_args=kunit.filter_glob=kunit_status
...
Testing complete. 2 tests run. 0 failed. 0 crashed. 0 skipped.

Signed-off-by: Daniel Latypov 
Reviewed-by: David Gow 
Reviewed-by: Brendan Higgins 
Signed-off-by: Shuah Khan