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Steven Rostedt (Google) ea82edad0a tracing: Do not free snapshot if tracer is on cmdline 
[ Upstream commit a541a9559b ]

The ftrace_boot_snapshot and alloc_snapshot cmdline options allocate the
snapshot buffer at boot up for use later. The ftrace_boot_snapshot in
particular requires the snapshot to be allocated because it will take a
snapshot at the end of boot up allowing to see the traces that happened
during boot so that it's not lost when user space takes over.

When a tracer is registered (started) there's a path that checks if it
requires the snapshot buffer or not, and if it does not and it was
allocated it will do a synchronization and free the snapshot buffer.

This is only required if the previous tracer was using it for "max
latency" snapshots, as it needs to make sure all max snapshots are
complete before freeing. But this is only needed if the previous tracer
was using the snapshot buffer for latency (like irqoff tracer and
friends). But it does not make sense to free it, if the previous tracer
was not using it, and the snapshot was allocated by the cmdline
parameters. This basically takes away the point of allocating it in the
first place!

Note, the allocated snapshot worked fine for just trace events, but fails
when a tracer is enabled on the cmdline.

Further investigation, this goes back even further and it does not require
a tracer on the cmdline to fail. Simply enable snapshots and then enable a
tracer, and it will remove the snapshot.

Link: https://lkml.kernel.org/r/20221005113757.041df7fe@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Fixes: 45ad21ca55 ("tracing: Have trace_array keep track if snapshot buffer is allocated")
Reported-by: Ross Zwisler <zwisler@kernel.org>
Tested-by: Ross Zwisler <zwisler@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-10-30 09:41:18 +01:00
arch iommu/vt-d: Allow NVS regions in arch_rmrr_sanity_check() 2022-10-30 09:41:17 +01:00
block blk-wbt: call rq_qos_add() after wb_normal is initialized 2022-10-30 09:41:16 +01:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:13:17 +02:00
crypto crypto: akcipher - default implementation for setting a private key 2022-10-26 13:25:42 +02:00
Documentation arm64: errata: Remove AES hwcap for COMPAT tasks 2022-10-30 09:41:16 +01:00
drivers dmaengine: mxs: use platform_driver_register 2022-10-30 09:41:18 +01:00
fs cifs: Fix xid leak in cifs_ses_add_channel() 2022-10-30 09:41:17 +01:00
include net: sched: delete duplicate cleanup of backlog and qlen 2022-10-30 09:41:17 +01:00
init Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug 2022-06-09 10:21:25 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:21:17 +02:00
kernel tracing: Do not free snapshot if tracer is on cmdline 2022-10-30 09:41:18 +01:00
lib dyndbg: drop EXPORTed dynamic_debug_exec_queries 2022-10-26 13:25:34 +02:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm: hugetlb: fix UAF in hugetlb_handle_userfault 2022-10-26 13:25:55 +02:00
net net: sched: fix race condition in qdisc_graft() 2022-10-30 09:41:17 +01:00
samples x86: Prepare inline-asm for straight-line-speculation 2022-07-25 11:26:29 +02:00
scripts kbuild: Add skip_encoding_btf_enum64 option to pahole 2022-10-28 12:57:12 +02:00
security selinux: enable use of both GFP_KERNEL and GFP_ATOMIC in convert_context() 2022-10-30 09:41:15 +01:00
sound ASoC: SOF: pci: Change DMI match info to support all Chrome platforms 2022-10-26 13:25:49 +02:00
tools perf intel-pt: Fix segfault in intel_pt_print_info() with uClibc 2022-10-26 13:25:54 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:25:48 +01:00
virt kvm: Add support for arch compat vm ioctls 2022-10-30 09:41:15 +01:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add Amir as xfs maintainer for 5.10.y 2022-07-02 16:39:22 +02:00
Makefile Linux 5.10.151 2022-10-28 13:02:36 +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.