[PATCH v2 00/13] Introduce seqnum_ops

Shuah Khan
2020-11-13T17:46:22Z

Sequence Number api provides interfaces for unsigned atomic up counters
leveraging atomic_t and atomic64_t ops underneath.

There are a number of atomic_t usages in the kernel where atomic_t api
is used for counting sequence numbers and other statistical counters.
Several of these usages, convert atomic_read() and atomic_inc_return()
return values to unsigned. Introducing sequence number ops supports
these use-cases with a standard core-api.

The atomic_t api provides a wide range of atomic operations as a base
api to implement atomic counters, bitops, spinlock interfaces. The usages
also evolved into being used for resource lifetimes and state management.
The refcount_t api was introduced to address resource lifetime problems
related to atomic_t wrapping. There is a large overlap between the
atomic_t api used for resource lifetimes and just counters, stats, and
sequence numbers. It has become difficult to differentiate between the
atomic_t usages that should be converted to refcount_t and the ones that
can be left alone. Introducing seqnum_ops to wrap the usages that are
stats, counters, sequence numbers makes it easier for tools that scan
for underflow and overflow on atomic_t usages to detect overflow and
underflows to scan just the cases that are prone to errors.

In addition, to supporting sequence number use-cases, Sequence Number Ops
helps differentiate atomic_t counter usages from atomic_t usages that guard
object lifetimes, hence prone to overflow and underflow errors from up
counting use-cases. It becomes easier for tools that scan for underflow and
overflow on atomic_t usages to detect overflow and underflows to scan just
the cases that are prone to errors.

Changes since v1:
- Removed dec based on Greg KH's comments
- Removed read/set/inc based on the discussion with Peter Zijlstra
- Interfaces are restricted to init, increment and return new value,
and fetch current value.
- Interfaces return u32 and u64 - a few reviewers suggested unsigned.
After reviewing a few use-cases, I determined this is a good path
forward. It adds unsigned atomic support that doesn't exist now,
and simplifies code in drivers that currently convert atomic_t return
values to unsigned. All the drivers changes included in this series
used to convert atomic_t returns to unsigned.

Patch v1 thread:
https://lore.kernel.org/lkml/cover.1605027593.git.skhan@linuxfoundation.org/

Counters thread:
lore.kernel.org/lkml/cover.1602209970.git.skhan@linuxfoundation.org

Shuah Khan (13):
seqnum_ops: Introduce Sequence Number Ops
selftests: lib:test_seqnum_ops: add new test for seqnum_ops
drivers/acpi: convert seqno seqnum_ops
drivers/acpi/apei: convert seqno to seqnum_ops
drivers/base/test/test_async_driver_probe: convert to use seqnum_ops
drivers/char/ipmi: convert stats to use seqnum_ops
drivers/edac: convert pci counters to seqnum_ops
drivers/oprofile: convert stats to use seqnum_ops
drivers/staging/rtl8723bs: convert stats to use seqnum_ops
usb: usbip/vhci: convert seqno to seqnum_ops
drivers/staging/rtl8188eu: convert stats to use seqnum_ops
drivers/staging/unisys/visorhba: convert stats to use seqnum_ops
security/integrity/ima: converts stats to seqnum_ops

Documentation/core-api/atomic_ops.rst | 4 +
Documentation/core-api/index.rst | 1 +
Documentation/core-api/seqnum_ops.rst | 89 +++++++++++++
MAINTAINERS | 8 ++
drivers/acpi/acpi_extlog.c | 8 +-
drivers/acpi/apei/ghes.c | 8 +-
drivers/base/test/test_async_driver_probe.c | 28 +++--
drivers/char/ipmi/ipmi_msghandler.c | 9 +-
drivers/char/ipmi/ipmi_si_intf.c | 9 +-
drivers/char/ipmi/ipmi_ssif.c | 9 +-
drivers/edac/edac_pci.h | 5 +-
drivers/edac/edac_pci_sysfs.c | 30 ++---
drivers/oprofile/buffer_sync.c | 9 +-
drivers/oprofile/event_buffer.c | 3 +-
drivers/oprofile/oprof.c | 3 +-
drivers/oprofile/oprofile_stats.c | 11 +-
drivers/oprofile/oprofile_stats.h | 11 +-
drivers/oprofile/oprofilefs.c | 3 +-
drivers/staging/rtl8188eu/core/rtw_mlme_ext.c | 23 +++-
.../staging/rtl8188eu/include/rtw_mlme_ext.h | 3 +-
drivers/staging/rtl8723bs/core/rtw_cmd.c | 3 +-
drivers/staging/rtl8723bs/core/rtw_mlme_ext.c | 33 +++--
drivers/staging/rtl8723bs/include/rtw_cmd.h | 3 +-
.../staging/rtl8723bs/include/rtw_mlme_ext.h | 3 +-
.../staging/unisys/visorhba/visorhba_main.c | 21 ++--
drivers/usb/usbip/vhci.h | 3 +-
drivers/usb/usbip/vhci_hcd.c | 7 +-
drivers/usb/usbip/vhci_rx.c | 5 +-
include/linux/oprofile.h | 3 +-
include/linux/seqnum_ops.h | 118 +++++++++++++++++
lib/Kconfig | 9 ++
lib/Makefile | 1 +
lib/test_seqnum_ops.c | 119 ++++++++++++++++++
security/integrity/ima/ima.h | 5 +-
security/integrity/ima/ima_api.c | 3 +-
security/integrity/ima/ima_fs.c | 5 +-
security/integrity/ima/ima_queue.c | 7 +-
tools/testing/selftests/lib/Makefile | 1 +
tools/testing/selftests/lib/config | 1 +
.../testing/selftests/lib/test_seqnum_ops.sh | 10 ++
40 files changed, 524 insertions(+), 110 deletions(-)
create mode 100644 Documentation/core-api/seqnum_ops.rst
create mode 100644 include/linux/seqnum_ops.h
create mode 100644 lib/test_seqnum_ops.c
create mode 100755 tools/testing/selftests/lib/test_seqnum_ops.sh

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2.27.0