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android/kernel/common/refs/tags/android16-6.12-2025-06_r17
tag
222e181d8091474c9edf3573287d6e3456f0eb5b
tagger
Howard Chen <howardsoc@google.com>
Thu Jul 31 14:43:45 2025 +0800
object
3b4b99596fcd3a30d2146c77b1d5572fcf867200
android16-6.12 June 2025 release 17

Artifacts:
  https://ci.android.com/builds/submitted/13859059/kernel_aarch64/latest
commit
3b4b99596fcd3a30d2146c77b1d5572fcf867200
[log]
author
Tze-nan Wu <Tze-nan.Wu@mediatek.com>
Thu Jul 17 13:53:38 2025 +0800
committer
Treehugger Robot <android-test-infra-autosubmit@system.gserviceaccount.com>
Wed Jul 30 11:59:22 2025 -0700
tree
d90163eab5fdc0e7c8314c095820db3c97d830ef
parent
2df0b8bf2a5e9cd0765a148901859dfdf7d9079a [diff]
FROMGIT: rcu: Fix delayed execution of hurry callbacks

We observed a regression in our customer’s environment after enabling
CONFIG_LAZY_RCU. In the Android Update Engine scenario, where ioctl() is
used heavily, we found that callbacks queued via call_rcu_hurry (such as
percpu_ref_switch_to_atomic_rcu) can sometimes be delayed by up to 5
seconds before execution. This occurs because the new grace period does
not start immediately after the previous one completes.

The root cause is that the wake_nocb_gp_defer() function now checks
"rdp->nocb_defer_wakeup" instead of "rdp_gp->nocb_defer_wakeup". On CPUs
that are not rcuog, "rdp->nocb_defer_wakeup" may always be
RCU_NOCB_WAKE_NOT. This can cause "rdp_gp->nocb_defer_wakeup" to be
downgraded and the "rdp_gp->nocb_timer" to be postponed by up to 10
seconds, delaying the execution of hurry RCU callbacks.

The trace log of one scenario we encountered is as follow:
  // previous GP ends at this point
  rcu_preempt   [000] d..1.   137.240210: rcu_grace_period: rcu_preempt 8369 end
  rcu_preempt   [000] .....   137.240212: rcu_grace_period: rcu_preempt 8372 reqwait
  // call_rcu_hurry enqueues "percpu_ref_switch_to_atomic_rcu", the callback waited on by UpdateEngine
  update_engine [002] d..1.   137.301593: __call_rcu_common: wyy: unlikely p_ref = 00000000********. lazy = 0
  // FirstQ on cpu 2 rdp_gp->nocb_timer is set to fire after 1 jiffy (4ms)
  // and the rdp_gp->nocb_defer_wakeup is set to RCU_NOCB_WAKE
  update_engine [002] d..2.   137.301595: rcu_nocb_wake: rcu_preempt 2 FirstQ on cpu2 with rdp_gp (cpu0).
  // FirstBQ event on cpu2 during the 1 jiffy, make the timer postpond 10 seconds later.
  // also, the rdp_gp->nocb_defer_wakeup is overwrite to RCU_NOCB_WAKE_LAZY
  update_engine [002] d..1.   137.301601: rcu_nocb_wake: rcu_preempt 2 WakeEmptyIsDeferred
  ...
  ...
  ...
  // before the 10 seconds timeout, cpu0 received another call_rcu_hurry
  // reset the timer to jiffies+1 and set the waketype = RCU_NOCB_WAKE.
  kworker/u32:0 [000] d..2.   142.557564: rcu_nocb_wake: rcu_preempt 0 FirstQ
  kworker/u32:0 [000] d..1.   142.557576: rcu_nocb_wake: rcu_preempt 0 WakeEmptyIsDeferred
  kworker/u32:0 [000] d..1.   142.558296: rcu_nocb_wake: rcu_preempt 0 WakeNot
  kworker/u32:0 [000] d..1.   142.558562: rcu_nocb_wake: rcu_preempt 0 WakeNot
  // idle(do_nocb_deferred_wakeup) wake rcuog due to waketype == RCU_NOCB_WAKE
  <idle>        [000] d..1.   142.558786: rcu_nocb_wake: rcu_preempt 0 DoWake
  <idle>        [000] dN.1.   142.558839: rcu_nocb_wake: rcu_preempt 0 DeferredWake
  rcuog/0       [000] .....   142.558871: rcu_nocb_wake: rcu_preempt 0 EndSleep
  rcuog/0       [000] .....   142.558877: rcu_nocb_wake: rcu_preempt 0 Check
  // finally rcuog request a new GP at this point (5 seconds after the FirstQ event)
  rcuog/0       [000] d..2.   142.558886: rcu_grace_period: rcu_preempt 8372 newreq
  rcu_preempt   [001] d..1.   142.559458: rcu_grace_period: rcu_preempt 8373 start
  ...
  rcu_preempt   [000] d..1.   142.564258: rcu_grace_period: rcu_preempt 8373 end
  rcuop/2       [000] D..1.   142.566337: rcu_batch_start: rcu_preempt CBs=219 bl=10
  // the hurry CB is invoked at this point
  rcuop/2       [000] b....   142.566352: blk_queue_usage_counter_release: wyy: wakeup. p_ref = 00000000********.

This patch changes the condition to check "rdp_gp->nocb_defer_wakeup" in
the lazy path. This prevents an already scheduled "rdp_gp->nocb_timer"
from being postponed and avoids overwriting "rdp_gp->nocb_defer_wakeup"
when it is not RCU_NOCB_WAKE_NOT.

Fixes: 3cb278e73be5 ("rcu: Make call_rcu() lazy to save power")
Co-developed-by: Cheng-jui Wang <cheng-jui.wang@mediatek.com>
Signed-off-by: Cheng-jui Wang <cheng-jui.wang@mediatek.com>
Co-developed-by: Lorry.Luo@mediatek.com
Signed-off-by: Lorry.Luo@mediatek.com
Tested-by: weiyangyang@vivo.com
Signed-off-by: weiyangyang@vivo.com
Signed-off-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>

Bug: 433659824
Bug: 434811509
Bug: 435082773
(cherry picked from commit 463d46044f04013306a4893242f65788b8a16b2e
 https://git.kernel.org/pub/scm/linux/kernel/git/neeraj.upadhyay/linux-rcu.git rcu.merge.22.07.2025)
Change-Id: I4a0cedfd3fe35f609262ba204f5fea2be2d5f9de
Signed-off-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
(cherry picked from commit d64d8b7dab32e1356e13ee75a26a6bd386d7cbc1)
1 file changed
tree: d90163eab5fdc0e7c8314c095820db3c97d830ef
  1. arch/
  2. block/
  3. certs/
  4. crypto/
  5. Documentation/
  6. drivers/
  7. fs/
  8. gki/
  9. include/
  10. init/
  11. io_uring/
  12. ipc/
  13. kernel/
  14. lib/
  15. LICENSES/
  16. mm/
  17. net/
  18. rust/
  19. samples/
  20. scripts/
  21. security/
  22. sound/
  23. tools/
  24. usr/
  25. virt/
  26. .bazelignore
  27. .clang-format
  28. .clippy.toml
  29. .cocciconfig
  30. .editorconfig
  31. .get_maintainer.ignore
  32. .gitattributes
  33. .gitignore
  34. .mailmap
  35. .rustfmt.toml
  36. abi.bzl
  37. BUILD.bazel
  38. build.config.aarch64
  39. build.config.arm
  40. build.config.common
  41. build.config.constants
  42. build.config.db845c
  43. build.config.gki
  44. build.config.gki.aarch64
  45. build.config.gki.x86_64
  46. build.config.rockpi4
  47. build.config.x86_64
  48. COPYING
  49. CREDITS
  50. Kbuild
  51. Kconfig
  52. Kconfig.ext
  53. MAINTAINERS
  54. Makefile
  55. modules.bzl
  56. OWNERS
  57. OWNERS_DrNo
  58. README
  59. README.md
README.md

How do I submit patches to Android Common Kernels

  1. BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.

    • Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux, additions of EXPORT_SYMBOL_GPL() require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export.
    • When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not a persuasive case.

  2. LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.

Common Kernel patch requirements

  • All patches must conform to the Linux kernel coding standards and pass scripts/checkpatch.pl
  • Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
  • If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch: UPSTREAM:, BACKPORT:, FROMGIT:, FROMLIST:, or ANDROID:.
  • All patches must have a Change-Id: tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html)
  • If an Android bug has been assigned, there must be a Bug: tag.
  • All patches must have a Signed-off-by: tag by the author and the submitter

Additional requirements are listed below based on patch type

Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:

  • If the patch is a cherry-pick from Linux mainline with no changes at all
    • tag the patch subject with UPSTREAM:.
    • add upstream commit information with a (cherry picked from commit ...) line
    • Example:
      • if the upstream commit message is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        UPSTREAM: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch requires any changes from the upstream version, tag the patch with BACKPORT: instead of UPSTREAM:.
    • use the same tags as UPSTREAM:
    • add comments about the changes under the (cherry picked from commit ...) line
    • Example:
        BACKPORT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        [joe: Resolved minor conflict in drivers/foo/bar.c ]
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for other backports: FROMGIT:, FROMLIST:,

  • If the patch has been merged into an upstream maintainer tree, but has not yet been merged into Linux mainline
    • tag the patch subject with FROMGIT:
    • add info on where the patch came from as (cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't use linux-next for example).
    • if changes were required, use BACKPORT: FROMGIT:
    • Example:
      • if the commit message in the maintainer tree is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        FROMGIT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        (cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
         https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch has been submitted to LKML, but not accepted into any maintainer tree
    • tag the patch subject with FROMLIST:
    • add a Link: tag with a link to the submittal on lore.kernel.org
    • add a Bug: tag with the Android bug (required for patches not accepted into a maintainer tree)
    • if changes were required, use BACKPORT: FROMLIST:
    • Example:
        FROMLIST: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If a patch has been submitted to the community, but rejected, do NOT use the FROMLIST: tag to try to hide this fact. Use the ANDROID: tag as described below as this must be considered as an Android-specific submission, not an upstream submission as the community will not accept these changes as-is.

Requirements for Android-specific patches: ANDROID:

  • If the patch is fixing a bug to Android-specific code
    • tag the patch subject with ANDROID:
    • add a Fixes: tag that cites the patch with the bug
    • Example:
        ANDROID: fix android-specific bug in foobar.c

        This is the detailed description of the important fix

        Fixes: 1234abcd2468 ("foobar: add cool feature")
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch is a new feature
    • tag the patch subject with ANDROID:
    • add a Bug: tag with the Android bug (required for android-specific features)