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Mathieu Desnoyers 09a44d994b ring-buffer: Fix 32-bit rb_time_read() race with rb_time_cmpxchg() 
[ Upstream commit dec890089b ]

The following race can cause rb_time_read() to observe a corrupted time
stamp:

rb_time_cmpxchg()
[...]
        if (!rb_time_read_cmpxchg(&t->msb, msb, msb2))
                return false;
        if (!rb_time_read_cmpxchg(&t->top, top, top2))
                return false;
<interrupted before updating bottom>
__rb_time_read()
[...]
        do {
                c = local_read(&t->cnt);
                top = local_read(&t->top);
                bottom = local_read(&t->bottom);
                msb = local_read(&t->msb);
        } while (c != local_read(&t->cnt));

        *cnt = rb_time_cnt(top);

        /* If top and msb counts don't match, this interrupted a write */
        if (*cnt != rb_time_cnt(msb))
                return false;
          ^ this check fails to catch that "bottom" is still not updated.

So the old "bottom" value is returned, which is wrong.

Fix this by checking that all three of msb, top, and bottom 2-bit cnt
values match.

The reason to favor checking all three fields over requiring a specific
update order for both rb_time_set() and rb_time_cmpxchg() is because
checking all three fields is more robust to handle partial failures of
rb_time_cmpxchg() when interrupted by nested rb_time_set().

Link: https://lore.kernel.org/lkml/20231211201324.652870-1-mathieu.desnoyers@efficios.com/
Link: https://lore.kernel.org/linux-trace-kernel/20231212193049.680122-1-mathieu.desnoyers@efficios.com

Fixes: f458a14534 ("ring-buffer: Test last update in 32bit version of __rb_time_read()")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-01-10 17:10:35 +01:00
arch s390/cpumf: support user space events for counting 2024-01-10 17:10:30 +01:00
block block: update the stable_writes flag in bdev_add 2024-01-10 17:10:32 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: pcrypt - Fix hungtask for PADATA_RESET 2023-11-28 17:06:58 +00:00
Documentation dt-bindings: nvmem: mxs-ocotp: Document fsl,ocotp 2024-01-01 12:39:04 +00:00
drivers octeontx2-af: Support variable number of lmacs 2024-01-10 17:10:34 +01:00
fs btrfs: mark the len field in struct btrfs_ordered_sum as unsigned 2024-01-10 17:10:35 +01:00
include net/sched: act_ct: Take per-cb reference to tcf_ct_flow_table 2024-01-10 17:10:34 +01:00
init proc: sysctl: prevent aliased sysctls from getting passed to init 2023-11-28 17:07:08 +00:00
io_uring net: Declare MSG_SPLICE_PAGES internal sendmsg() flag 2024-01-10 17:10:27 +01:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel ring-buffer: Fix 32-bit rb_time_read() race with rb_time_cmpxchg() 2024-01-10 17:10:35 +01:00
lib lib/group_cpus.c: avoid acquiring cpu hotplug lock in group_cpus_evenly 2024-01-10 17:10:33 +01:00
LICENSES
mm mm/memory_hotplug: fix error handling in add_memory_resource() 2024-01-10 17:10:33 +01:00
net net/sched: act_ct: Take per-cb reference to tcf_ct_flow_table 2024-01-10 17:10:34 +01:00
rust rust: allocator: Prevent mis-aligned allocation 2023-08-11 12:08:18 +02:00
samples fprobe: Pass entry_data to handlers 2023-10-25 12:03:12 +02:00
scripts sign-file: Fix incorrect return values check 2023-12-20 17:00:19 +01:00
security keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry 2024-01-01 12:38:58 +00:00
sound ALSA: hda/realtek: Add quirk for Lenovo Yoga Pro 7 2024-01-10 17:10:32 +01:00
tools selftests: mptcp: set FAILING_LINKS in run_tests 2024-01-10 17:10:31 +01:00
usr
virt kvm/vfio: ensure kvg instance stays around in kvm_vfio_group_add() 2023-09-13 09:42:46 +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
.gitattributes
.gitignore
.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
COPYING
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild
Kconfig
MAINTAINERS genirq/affinity: Move group_cpus_evenly() into lib/ 2024-01-10 17:10:33 +01:00
Makefile Linux 6.1.71 2024-01-05 15:18:41 +01:00
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.