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