tjh.dev/kernel at a3c3c66670cee11eb13aa43905904bf29cb92d32

The perf events code fails to account for total_time_enabled of
inactive events.

Here is a failure case for accounting total_time_enabled for
CPU PMU events:

sudo ./perf stat -vvv -e armv8_pmuv3_0/event=0x08/ -e armv8_pmuv3_1/event=0x08/ -- stress-ng --pthread=2 -t 2s
...

armv8_pmuv3_0/event=0x08/: 1138698008 2289429840 2174835740
armv8_pmuv3_1/event=0x08/: 1826791390 1950025700 847648440
` ` `
` ` > total_time_running with child
` > total_time_enabled with child
> count with child

Performance counter stats for 'stress-ng --pthread=2 -t 2s':

1,138,698,008 armv8_pmuv3_0/event=0x08/ (94.99%)
1,826,791,390 armv8_pmuv3_1/event=0x08/ (43.47%)

The two events above are opened on two different CPU PMUs, for example,
each event is opened for a cluster in an Arm big.LITTLE system, they
will never run on the same CPU. In theory, the total enabled time should
be same for both events, as two events are opened and closed together.

As the result show, the two events' total enabled time including
child event is different (2289429840 vs 1950025700).

This is because child events are not accounted properly
if a event is INACTIVE state when the task exits:

perf_event_exit_event()
`> perf_remove_from_context()
`> __perf_remove_from_context()
`> perf_child_detach() -> Accumulate child_total_time_enabled
`> list_del_event() -> Update child event's time

The problem is the time accumulation happens prior to child event's
time updating. Thus, it misses to account the last period's time when
the event exits.

The perf core layer follows the rule that timekeeping is tied to state
change. To address the issue, make __perf_remove_from_context()
handle the task exit case by passing 'DETACH_EXIT' to it and
invoke perf_event_state() for state alongside with accounting the time.

Then, perf_child_detach() populates the time into the parent's time metrics.

After this patch, the bug is fixed:

sudo ./perf stat -vvv -e armv8_pmuv3_0/event=0x08/ -e armv8_pmuv3_1/event=0x08/ -- stress-ng --pthread=2 -t 10s
...
armv8_pmuv3_0/event=0x08/: 15396770398 32157963940 21898169000
armv8_pmuv3_1/event=0x08/: 22428964974 32157963940 10259794940

Performance counter stats for 'stress-ng --pthread=2 -t 10s':

15,396,770,398 armv8_pmuv3_0/event=0x08/ (68.10%)
22,428,964,974 armv8_pmuv3_1/event=0x08/ (31.90%)

[ mingo: Clarified the changelog. ]

Fixes: ef54c1a476aef ("perf: Rework perf_event_exit_event()")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/r/20250326082003.1630986-1-yeoreum.yun@arm.com

a3c3c666

Yeoreum Yun

1 year ago

Merge tag 'rust-6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull Rust updates from Miguel Ojeda:
"Toolchain and infrastructure:

- Extract the 'pin-init' API from the 'kernel' crate and make it into
a standalone crate.

In order to do this, the contents are rearranged so that they can
easily be kept in sync with the version maintained out-of-tree that
other projects have started to use too (or plan to, like QEMU).

This will reduce the maintenance burden for Benno, who will now
have his own sub-tree, and will simplify future expected changes
like the move to use 'syn' to simplify the implementation.

- Add '#[test]'-like support based on KUnit.

We already had doctests support based on KUnit, which takes the
examples in our Rust documentation and runs them under KUnit.

Now, we are adding the beginning of the support for "normal" tests,
similar to those the '#[test]' tests in userspace Rust. For
instance:

#[kunit_tests(my_suite)]
mod tests {
#[test]
fn my_test() {
assert_eq!(1 + 1, 2);
}
}

Unlike with doctests, the 'assert*!'s do not map to the KUnit
assertion APIs yet.

- Check Rust signatures at compile time for functions called from C
by name.

In particular, introduce a new '#[export]' macro that can be placed
in the Rust function definition. It will ensure that the function
declaration on the C side matches the signature on the Rust
function:

#[export]
pub unsafe extern "C" fn my_function(a: u8, b: i32) -> usize {
// ...
}

The macro essentially forces the compiler to compare the types of
the actual Rust function and the 'bindgen'-processed C signature.

These cases are rare so far. In the future, we may consider
introducing another tool, 'cbindgen', to generate C headers
automatically. Even then, having these functions explicitly marked
may be a good idea anyway.

- Enable the 'raw_ref_op' Rust feature: it is already stable, and
allows us to use the new '&raw' syntax, avoiding a couple macros.
After everyone has migrated, we will disallow the macros.

- Pass the correct target to 'bindgen' on Usermode Linux.

- Fix 'rusttest' build in macOS.

'kernel' crate:

- New 'hrtimer' module: add support for setting up intrusive timers
without allocating when starting the timer. Add support for
'Pin<Box<_>>', 'Arc<_>', 'Pin<&_>' and 'Pin<&mut _>' as pointer
types for use with timer callbacks. Add support for setting clock
source and timer mode.

- New 'dma' module: add a simple DMA coherent allocator abstraction
and a test sample driver.

- 'list' module: make the linked list 'Cursor' point between
elements, rather than at an element, which is more convenient to us
and allows for cursors to empty lists; and document it with
examples of how to perform common operations with the provided
methods.

- 'str' module: implement a few traits for 'BStr' as well as the
'strip_prefix()' method.

- 'sync' module: add 'Arc::as_ptr'.

- 'alloc' module: add 'Box::into_pin'.

- 'error' module: extend the 'Result' documentation, including a few
examples on different ways of handling errors, a warning about
using methods that may panic, and links to external documentation.

'macros' crate:

- 'module' macro: add the 'authors' key to support multiple authors.
The original key will be kept until everyone has migrated.

Documentation:

- Add error handling sections.

MAINTAINERS:

- Add Danilo Krummrich as reviewer of the Rust "subsystem".

- Add 'RUST [PIN-INIT]' entry with Benno Lossin as maintainer. It has
its own sub-tree.

- Add sub-tree for 'RUST [ALLOC]'.

- Add 'DMA MAPPING HELPERS DEVICE DRIVER API [RUST]' entry with
Abdiel Janulgue as primary maintainer. It will go through the
sub-tree of the 'RUST [ALLOC]' entry.

- Add 'HIGH-RESOLUTION TIMERS [RUST]' entry with Andreas Hindborg as
maintainer. It has its own sub-tree.

And a few other cleanups and improvements"

* tag 'rust-6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux: (71 commits)
rust: dma: add `Send` implementation for `CoherentAllocation`
rust: macros: fix `make rusttest` build on macOS
rust: block: refactor to use `&raw mut`
rust: enable `raw_ref_op` feature
rust: uaccess: name the correct function
rust: rbtree: fix comments referring to Box instead of KBox
rust: hrtimer: add maintainer entry
rust: hrtimer: add clocksource selection through `ClockId`
rust: hrtimer: add `HrTimerMode`
rust: hrtimer: implement `HrTimerPointer` for `Pin<Box<T>>`
rust: alloc: add `Box::into_pin`
rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`
rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&T>`
rust: hrtimer: add `hrtimer::ScopedHrTimerPointer`
rust: hrtimer: add `UnsafeHrTimerPointer`
rust: hrtimer: allow timer restart from timer handler
rust: str: implement `strip_prefix` for `BStr`
rust: str: implement `AsRef<BStr>` for `[u8]` and `BStr`
rust: str: implement `Index` for `BStr`
rust: str: implement `PartialEq` for `BStr`
...

4e82c870

Linus Torvalds

1 year ago

Merge tag 'modules-6.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/modules/linux

01d5b167

Linus Torvalds

1 year ago

Merge tag 'rust-hrtimer-for-v6.15-v3' of https://github.com/Rust-for-Linux/linux into rust-next

e6ea10d5

Miguel Ojeda

1 year ago

Merge tag 'x86-urgent-2025-03-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

7405c0f0

Linus Torvalds

1 year ago

MAINTAINERS: Update the MODULE SUPPORT section

897c0b4e

Petr Pavlu

1 year ago

rust: dma: add `Send` implementation for `CoherentAllocation`

28bb48c4

Danilo Krummrich

1 year ago

rust: hrtimer: add maintainer entry

142d9391

Andreas Hindborg

1 year ago

Merge tag 'locking-urgent-2025-03-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

b4c5c57c

Linus Torvalds

1 year ago

x86/microcode/AMD: Fix __apply_microcode_amd()'s return value

31ab12df

Boris Ostrovsky

1 year ago

module: Remove unnecessary size argument when calling strscpy()

085c5e37

Thorsten Blum

1 year ago

rust: macros: fix `make rusttest` build on macOS

a0b539ad

Tamir Duberstein

1 year ago

rust: hrtimer: add clocksource selection through `ClockId`

aa33de03

Andreas Hindborg

1 year ago

Merge tag 'bpf_try_alloc_pages' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next

Pull bpf try_alloc_pages() support from Alexei Starovoitov:
"The pull includes work from Sebastian, Vlastimil and myself with a lot
of help from Michal and Shakeel.

This is a first step towards making kmalloc reentrant to get rid of
slab wrappers: bpf_mem_alloc, kretprobe's objpool, etc. These patches
make page allocator safe from any context.

Vlastimil kicked off this effort at LSFMM 2024:

https://lwn.net/Articles/974138/

and we continued at LSFMM 2025:

https://lore.kernel.org/all/CAADnVQKfkGxudNUkcPJgwe3nTZ=xohnRshx9kLZBTmR_E1DFEg@mail.gmail.com/

Why:

SLAB wrappers bind memory to a particular subsystem making it
unavailable to the rest of the kernel. Some BPF maps in production
consume Gbytes of preallocated memory. Top 5 in Meta: 1.5G, 1.2G,
1.1G, 300M, 200M. Once we have kmalloc that works in any context BPF
map preallocation won't be necessary.

How:

Synchronous kmalloc/page alloc stack has multiple stages going from
fast to slow: cmpxchg16 -> slab_alloc -> new_slab -> alloc_pages ->
rmqueue_pcplist -> __rmqueue, where rmqueue_pcplist was already
relying on trylock.

This set changes rmqueue_bulk/rmqueue_buddy to attempt a trylock and
return ENOMEM if alloc_flags & ALLOC_TRYLOCK. It then wraps this
functionality into try_alloc_pages() helper. We make sure that the
logic is sane in PREEMPT_RT.

End result: try_alloc_pages()/free_pages_nolock() are safe to call
from any context.

try_kmalloc() for any context with similar trylock approach will
follow. It will use try_alloc_pages() when slab needs a new page.
Though such try_kmalloc/page_alloc() is an opportunistic allocator,
this design ensures that the probability of successful allocation of
small objects (up to one page in size) is high.

Even before we have try_kmalloc(), we already use try_alloc_pages() in
BPF arena implementation and it's going to be used more extensively in
BPF"

* tag 'bpf_try_alloc_pages' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next:
mm: Fix the flipped condition in gfpflags_allow_spinning()
bpf: Use try_alloc_pages() to allocate pages for bpf needs.
mm, bpf: Use memcg in try_alloc_pages().
memcg: Use trylock to access memcg stock_lock.
mm, bpf: Introduce free_pages_nolock()
mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation
locking/local_lock: Introduce localtry_lock_t

aa918db7

Linus Torvalds

1 year ago

locking/lockdep: Decrease nr_unused_locks if lock unused in zap_class()

495f53d5

Boqun Feng

1 year ago

x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()

If track_pfn_copy() fails, we already added the dst VMA to the maple
tree. As fork() fails, we'll cleanup the maple tree, and stumble over
the dst VMA for which we neither performed any reservation nor copied
any page tables.

Consequently untrack_pfn() will see VM_PAT and try obtaining the
PAT information from the page table -- which fails because the page
table was not copied.

The easiest fix would be to simply clear the VM_PAT flag of the dst VMA
if track_pfn_copy() fails. However, the whole thing is about "simply"
clearing the VM_PAT flag is shaky as well: if we passed track_pfn_copy()
and performed a reservation, but copying the page tables fails, we'll
simply clear the VM_PAT flag, not properly undoing the reservation ...
which is also wrong.

So let's fix it properly: set the VM_PAT flag only if the reservation
succeeded (leaving it clear initially), and undo the reservation if
anything goes wrong while copying the page tables: clearing the VM_PAT
flag after undoing the reservation.

Note that any copied page table entries will get zapped when the VMA will
get removed later, after copy_page_range() succeeded; as VM_PAT is not set
then, we won't try cleaning VM_PAT up once more and untrack_pfn() will be
happy. Note that leaving these page tables in place without a reservation
is not a problem, as we are aborting fork(); this process will never run.

A reproducer can trigger this usually at the first try:

https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/reproducers/pat_fork.c

WARNING: CPU: 26 PID: 11650 at arch/x86/mm/pat/memtype.c:983 get_pat_info+0xf6/0x110
Modules linked in: ...
CPU: 26 UID: 0 PID: 11650 Comm: repro3 Not tainted 6.12.0-rc5+ #92
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014
RIP: 0010:get_pat_info+0xf6/0x110
...
Call Trace:
<TASK>
...
untrack_pfn+0x52/0x110
unmap_single_vma+0xa6/0xe0
unmap_vmas+0x105/0x1f0
exit_mmap+0xf6/0x460
__mmput+0x4b/0x120
copy_process+0x1bf6/0x2aa0
kernel_clone+0xab/0x440
__do_sys_clone+0x66/0x90
do_syscall_64+0x95/0x180

Likely this case was missed in:

d155df53f310 ("x86/mm/pat: clear VM_PAT if copy_p4d_range failed")

... and instead of undoing the reservation we simply cleared the VM_PAT flag.

Keep the documentation of these functions in include/linux/pgtable.h,
one place is more than sufficient -- we should clean that up for the other
functions like track_pfn_remap/untrack_pfn separately.

Fixes: d155df53f310 ("x86/mm/pat: clear VM_PAT if copy_p4d_range failed")
Fixes: 2ab640379a0a ("x86: PAT: hooks in generic vm code to help archs to track pfnmap regions - v3")
Reported-by: xingwei lee <xrivendell7@gmail.com>
Reported-by: yuxin wang <wang1315768607@163.com>
Reported-by: Marius Fleischer <fleischermarius@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20250321112323.153741-1-david@redhat.com
Closes: https://lore.kernel.org/lkml/CABOYnLx_dnqzpCW99G81DmOr+2UzdmZMk=T3uxwNxwz+R1RAwg@mail.gmail.com/
Closes: https://lore.kernel.org/lkml/CAJg=8jwijTP5fre8woS4JVJQ8iUA6v+iNcsOgtj9Zfpc3obDOQ@mail.gmail.com/

dc84bc2a

David Hildenbrand

1 year ago

branches 3

master 14 hours ago default

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v7.0

1 week ago latest

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.

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