mirrors/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2024-09-24 19:35:58 +00:00
Code Issues Releases Wiki Activity
No description
1153941 commits 105 branches 5097 tags 5.5 GiB
C 97.6%
Assembly 1%
Shell 0.5%
Python 0.3%
Makefile 0.3%
Find a file
Steven Rostedt (Google) 2d5f12de4c ring-buffer: Only update pages_touched when a new page is touched 
commit ffe3986fec upstream.

The "buffer_percent" logic that is used by the ring buffer splice code to
only wake up the tasks when there's no data after the buffer is filled to
the percentage of the "buffer_percent" file is dependent on three
variables that determine the amount of data that is in the ring buffer:

 1) pages_read - incremented whenever a new sub-buffer is consumed
 2) pages_lost - incremented every time a writer overwrites a sub-buffer
 3) pages_touched - incremented when a write goes to a new sub-buffer

The percentage is the calculation of:

  (pages_touched - (pages_lost + pages_read)) / nr_pages

Basically, the amount of data is the total number of sub-bufs that have been
touched, minus the number of sub-bufs lost and sub-bufs consumed. This is
divided by the total count to give the buffer percentage. When the
percentage is greater than the value in the "buffer_percent" file, it
wakes up splice readers waiting for that amount.

It was observed that over time, the amount read from the splice was
constantly decreasing the longer the trace was running. That is, if one
asked for 60%, it would read over 60% when it first starts tracing, but
then it would be woken up at under 60% and would slowly decrease the
amount of data read after being woken up, where the amount becomes much
less than the buffer percent.

This was due to an accounting of the pages_touched incrementation. This
value is incremented whenever a writer transfers to a new sub-buffer. But
the place where it was incremented was incorrect. If a writer overflowed
the current sub-buffer it would go to the next one. If it gets preempted
by an interrupt at that time, and the interrupt performs a trace, it too
will end up going to the next sub-buffer. But only one should increment
the counter. Unfortunately, that was not the case.

Change the cmpxchg() that does the real switch of the tail-page into a
try_cmpxchg(), and on success, perform the increment of pages_touched. This
will only increment the counter once for when the writer moves to a new
sub-buffer, and not when there's a race and is incremented for when a
writer and its preempting writer both move to the same new sub-buffer.

Link: https://lore.kernel.org/linux-trace-kernel/20240409151309.0d0e5056@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: 2c2b0a78b3 ("ring-buffer: Add percentage of ring buffer full to wake up reader")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-04-17 11:18:22 +02:00
arch perf/x86/amd/lbr: Discard erroneous branch entries 2024-04-13 13:05:15 +02:00
block block: prevent division by zero in blk_rq_stat_sum() 2024-04-13 13:05:12 +02:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: jitter - fix CRYPTO_JITTERENTROPY help text 2024-03-26 18:20:50 -04:00
Documentation x86/bhi: Mitigate KVM by default 2024-04-10 16:28:35 +02:00
drivers ata: libata-scsi: Fix ata_scsi_dev_rescan() error path 2024-04-17 11:18:22 +02:00
fs smb3: fix Open files on server counter going negative 2024-04-17 11:18:22 +02:00
include net: mpls: error out if inner headers are not set 2024-04-13 13:05:27 +02:00
init init: open /initrd.image with O_LARGEFILE 2024-04-03 15:19:47 +02:00
io_uring io_uring: clear opcode specific data for an early failure 2024-04-13 13:05:20 +02:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel ring-buffer: Only update pages_touched when a new page is touched 2024-04-17 11:18:22 +02:00
lib pci_iounmap(): Fix MMIO mapping leak 2024-04-03 15:19:25 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm x86/mm/pat: fix VM_PAT handling in COW mappings 2024-04-10 16:28:33 +02:00
net batman-adv: Avoid infinite loop trying to resize local TT 2024-04-17 11:18:22 +02:00
rust rust: allocator: Prevent mis-aligned allocation 2023-08-11 12:08:18 +02:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:12:28 +01:00
scripts gcc-plugins/stackleak: Avoid .head.text section 2024-04-13 13:05:23 +02:00
security landlock: Warn once if a Landlock action is requested while disabled 2024-04-03 15:19:32 +02:00
sound ASoC: soc-core.c: Skip dummy codec when adding platforms 2024-04-13 13:05:19 +02:00
tools tools: iio: replace seekdir() in iio_generic_buffer 2024-04-13 13:05:16 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Always flush async #PF workqueue when vCPU is being destroyed 2024-04-03 15:19:25 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS trace: Relocate event helper files 2024-03-06 14:45:17 +00:00
Makefile Linux 6.1.86 2024-04-13 13:05:29 +02:00
README

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 Restructured Text 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.