There is race issue when concurrently splice_read main trace_pipe and
per_cpu trace_pipes which will result in data read out being different
from what actually writen.

As suggested by Steven:
  > I believe we should add a ref count to trace_pipe and the per_cpu
  > trace_pipes, where if they are opened, nothing else can read it.
  >
  > Opening trace_pipe locks all per_cpu ref counts, if any of them are
  > open, then the trace_pipe open will fail (and releases any ref counts
  > it had taken).
  >
  > Opening a per_cpu trace_pipe will up the ref count for just that
  > CPU buffer. This will allow multiple tasks to read different per_cpu
  > trace_pipe files, but will prevent the main trace_pipe file from
  > being opened.

But because we only need to know whether per_cpu trace_pipe is open or
not, using a cpumask instead of using ref count may be easier.

After this patch, users will find that:
 - Main trace_pipe can be opened by only one user, and if it is
   opened, all per_cpu trace_pipes cannot be opened;
 - Per_cpu trace_pipes can be opened by multiple users, but each per_cpu
   trace_pipe can only be opened by one user. And if one of them is
   opened, main trace_pipe cannot be opened.

Link: https://lore.kernel.org/linux-trace-kernel/20230818022645.1948314-1-zhengyejian1@huawei.com

Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Kmemleak report a leak in graph_trace_open():

  unreferenced object 0xffff0040b95f4a00 (size 128):
    comm "cat", pid 204981, jiffies 4301155872 (age 99771.964s)
    hex dump (first 32 bytes):
      e0 05 e7 b4 ab 7d 00 00 0b 00 01 00 00 00 00 00 .....}..........
      f4 00 01 10 00 a0 ff ff 00 00 00 00 65 00 10 00 ............e...
    backtrace:
      [<000000005db27c8b>] kmem_cache_alloc_trace+0x348/0x5f0
      [<000000007df90faa>] graph_trace_open+0xb0/0x344
      [<00000000737524cd>] __tracing_open+0x450/0xb10
      [<0000000098043327>] tracing_open+0x1a0/0x2a0
      [<00000000291c3876>] do_dentry_open+0x3c0/0xdc0
      [<000000004015bcd6>] vfs_open+0x98/0xd0
      [<000000002b5f60c9>] do_open+0x520/0x8d0
      [<00000000376c7820>] path_openat+0x1c0/0x3e0
      [<00000000336a54b5>] do_filp_open+0x14c/0x324
      [<000000002802df13>] do_sys_openat2+0x2c4/0x530
      [<0000000094eea458>] __arm64_sys_openat+0x130/0x1c4
      [<00000000a71d7881>] el0_svc_common.constprop.0+0xfc/0x394
      [<00000000313647bf>] do_el0_svc+0xac/0xec
      [<000000002ef1c651>] el0_svc+0x20/0x30
      [<000000002fd4692a>] el0_sync_handler+0xb0/0xb4
      [<000000000c309c35>] el0_sync+0x160/0x180

The root cause is descripted as follows:

  __tracing_open() {  // 1. File 'trace' is being opened;
    ...
    *iter->trace = *tr->current_trace;  // 2. Tracer 'function_graph' is
                                        //    currently set;
    ...
    iter->trace->open(iter);  // 3. Call graph_trace_open() here,
                              //    and memory are allocated in it;
    ...
  }

  s_start() {  // 4. The opened file is being read;
    ...
    *iter->trace = *tr->current_trace;  // 5. If tracer is switched to
                                        //    'nop' or others, then memory
                                        //    in step 3 are leaked!!!
    ...
  }

To fix it, in s_start(), close tracer before switching then reopen the
new tracer after switching. And some tracers like 'wakeup' may not update
'iter->private' in some cases when reopen, then it should be cleared
to avoid being mistakenly closed again.

Link: https://lore.kernel.org/linux-trace-kernel/20230817125539.1646321-1-zhengyejian1@huawei.com

Fixes: d7350c3f4569 ("tracing/core: make the read callbacks reentrants")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

While debugging another issue I noticed that the stack trace contains one
invalid entry at the end:

<idle>-0       [008] d..4.    26.484201: wake_lat: pid=0 delta=2629976084 000000009cc24024 stack=STACK:
=> __schedule+0xac6/0x1a98
=> schedule+0x126/0x2c0
=> schedule_timeout+0x150/0x2c0
=> kcompactd+0x9ca/0xc20
=> kthread+0x2f6/0x3d8
=> __ret_from_fork+0x8a/0xe8
=> 0x6b6b6b6b6b6b6b6b

This is because the code failed to add the one element containing the
number of entries to field_size.

Link: https://lkml.kernel.org/r/20230816154928.4171614-4-svens@linux.ibm.com

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 00cf3d672a9d ("tracing: Allow synthetic events to pass around stacktraces")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

While debugging another issue I noticed that the stack trace output
contains the number of entries on top:

         <idle>-0       [000] d..4.   203.322502: wake_lat: pid=0 delta=2268270616 stack=STACK:
=> 0x10
=> __schedule+0xac6/0x1a98
=> schedule+0x126/0x2c0
=> schedule_timeout+0x242/0x2c0
=> __wait_for_common+0x434/0x680
=> __wait_rcu_gp+0x198/0x3e0
=> synchronize_rcu+0x112/0x138
=> ring_buffer_reset_online_cpus+0x140/0x2e0
=> tracing_reset_online_cpus+0x15c/0x1d0
=> tracing_set_clock+0x180/0x1d8
=> hist_register_trigger+0x486/0x670
=> event_hist_trigger_parse+0x494/0x1318
=> trigger_process_regex+0x1d4/0x258
=> event_trigger_write+0xb4/0x170
=> vfs_write+0x210/0xad0
=> ksys_write+0x122/0x208

Fix this by skipping the first element. Also replace the pointer
logic with an index variable which is easier to read.

Link: https://lkml.kernel.org/r/20230816154928.4171614-3-svens@linux.ibm.com

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 00cf3d672a9d ("tracing: Allow synthetic events to pass around stacktraces")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

The current code uses a lot of casts to access the fields member in struct
synth_trace_events with different sizes.  This makes the code hard to
read, and had already introduced an endianness bug. Use a union and struct
instead.

Link: https://lkml.kernel.org/r/20230816154928.4171614-2-svens@linux.ibm.com

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 00cf3d672a9dd ("tracing: Allow synthetic events to pass around stacktraces")
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Trace ring buffer can no longer record anything after executing
following commands at the shell prompt:

  # cd /sys/kernel/tracing
  # cat tracing_cpumask
  fff
  # echo 0 > tracing_cpumask
  # echo 1 > snapshot
  # echo fff > tracing_cpumask
  # echo 1 > tracing_on
  # echo "hello world" > trace_marker
  -bash: echo: write error: Bad file descriptor

The root cause is that:
  1. After `echo 0 > tracing_cpumask`, 'record_disabled' of cpu buffers
     in 'tr->array_buffer.buffer' became 1 (see tracing_set_cpumask());
  2. After `echo 1 > snapshot`, 'tr->array_buffer.buffer' is swapped
     with 'tr->max_buffer.buffer', then the 'record_disabled' became 0
     (see update_max_tr());
  3. After `echo fff > tracing_cpumask`, the 'record_disabled' become -1;
Then array_buffer and max_buffer are both unavailable due to value of
'record_disabled' is not 0.

To fix it, enable or disable both array_buffer and max_buffer at the same
time in tracing_set_cpumask().

Link: https://lkml.kernel.org/r/20230805033816.3284594-2-zhengyejian1@huawei.com

Cc: <mhiramat@kernel.org>
Cc: <vnagarnaik@google.com>
Cc: <shuah@kernel.org>
Fixes: 71babb2705e2 ("tracing: change CPU ring buffer state from tracing_cpumask")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Pull networking fixes from Jakub Kicinski:
 "Including fixes from bpf and wireless.

  Nothing scary here. Feels like the first wave of regressions from v6.5
  is addressed - one outstanding fix still to come in TLS for the
  sendpage rework.

  Current release - regressions:

   - udp: fix __ip_append_data()'s handling of MSG_SPLICE_PAGES

   - dsa: fix older DSA drivers using phylink

  Previous releases - regressions:

   - gro: fix misuse of CB in udp socket lookup

   - mlx5: unregister devlink params in case interface is down

   - Revert "wifi: ath11k: Enable threaded NAPI"

  Previous releases - always broken:

   - sched: cls_u32: fix match key mis-addressing

   - sched: bind logic fixes for cls_fw, cls_u32 and cls_route

   - add bound checks to a number of places which hand-parse netlink

   - bpf: disable preemption in perf_event_output helpers code

   - qed: fix scheduling in a tasklet while getting stats

   - avoid using APIs which are not hardirq-safe in couple of drivers,
     when we may be in a hard IRQ (netconsole)

   - wifi: cfg80211: fix return value in scan logic, avoid page
     allocator warning

   - wifi: mt76: mt7615: do not advertise 5 GHz on first PHY of MT7615D
     (DBDC)

  Misc:

   - drop handful of inactive maintainers, put some new in place"

* tag 'net-6.5-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (98 commits)
  MAINTAINERS: update TUN/TAP maintainers
  test/vsock: remove vsock_perf executable on `make clean`
  tcp_metrics: fix data-race in tcpm_suck_dst() vs fastopen
  tcp_metrics: annotate data-races around tm->tcpm_net
  tcp_metrics: annotate data-races around tm->tcpm_vals[]
  tcp_metrics: annotate data-races around tm->tcpm_lock
  tcp_metrics: annotate data-races around tm->tcpm_stamp
  tcp_metrics: fix addr_same() helper
  prestera: fix fallback to previous version on same major version
  udp: Fix __ip_append_data()'s handling of MSG_SPLICE_PAGES
  net/mlx5e: Set proper IPsec source port in L4 selector
  net/mlx5: fs_core: Skip the FTs in the same FS_TYPE_PRIO_CHAINS fs_prio
  net/mlx5: fs_core: Make find_closest_ft more generic
  wifi: brcmfmac: Fix field-spanning write in brcmf_scan_params_v2_to_v1()
  vxlan: Fix nexthop hash size
  ip6mr: Fix skb_under_panic in ip6mr_cache_report()
  s390/qeth: Don't call dev_close/dev_open (DOWN/UP)
  net: tap_open(): set sk_uid from current_fsuid()
  net: tun_chr_open(): set sk_uid from current_fsuid()
  net: dcb: choose correct policy to parse DCB_ATTR_BCN
  ...

Martin KaFai Lau says:

====================
pull-request: bpf 2023-08-03

We've added 5 non-merge commits during the last 7 day(s) which contain
a total of 3 files changed, 37 insertions(+), 20 deletions(-).

The main changes are:

1) Disable preemption in perf_event_output helpers code,
   from Jiri Olsa

2) Add length check for SK_DIAG_BPF_STORAGE_REQ_MAP_FD parsing,
   from Lin Ma

3) Multiple warning splat fixes in cpumap from Hou Tao

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
  bpf, cpumap: Handle skb as well when clean up ptr_ring
  bpf, cpumap: Make sure kthread is running before map update returns
  bpf: Add length check for SK_DIAG_BPF_STORAGE_REQ_MAP_FD parsing
  bpf: Disable preemption in bpf_event_output
  bpf: Disable preemption in bpf_perf_event_output
====================

Link: https://lore.kernel.org/r/20230803181429.994607-1-martin.lau@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Pull probe fixes from Masami Hiramatsu:

 - probe-events: add NULL check for some BTF API calls which can return
   error code and NULL.

 - ftrace selftests: check fprobe and kprobe event correctly. This fixes
   a miss condition of the test command.

 - kprobes: do not allow probing functions that start with "__cfi_" or
   "__pfx_" since those are auto generated for kernel CFI and not
   executed.

* tag 'probes-fixes-v6.5-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  kprobes: Prohibit probing on CFI preamble symbol
  selftests/ftrace: Fix to check fprobe event eneblement
  tracing/probes: Fix to add NULL check for BTF APIs

Warning happened in trace_buffered_event_disable() at
  WARN_ON_ONCE(!trace_buffered_event_ref)

  Call Trace:
   ? __warn+0xa5/0x1b0
   ? trace_buffered_event_disable+0x189/0x1b0
   __ftrace_event_enable_disable+0x19e/0x3e0
   free_probe_data+0x3b/0xa0
   unregister_ftrace_function_probe_func+0x6b8/0x800
   event_enable_func+0x2f0/0x3d0
   ftrace_process_regex.isra.0+0x12d/0x1b0
   ftrace_filter_write+0xe6/0x140
   vfs_write+0x1c9/0x6f0
   [...]

The cause of the warning is in __ftrace_event_enable_disable(),
trace_buffered_event_enable() was called once while
trace_buffered_event_disable() was called twice.
Reproduction script show as below, for analysis, see the comments:
 ```
 #!/bin/bash

 cd /sys/kernel/tracing/

 # 1. Register a 'disable_event' command, then:
 #    1) SOFT_DISABLED_BIT was set;
 #    2) trace_buffered_event_enable() was called first time;
 echo 'cmdline_proc_show:disable_event:initcall:initcall_finish' > \
     set_ftrace_filter

 # 2. Enable the event registered, then:
 #    1) SOFT_DISABLED_BIT was cleared;
 #    2) trace_buffered_event_disable() was called first time;
 echo 1 > events/initcall/initcall_finish/enable

 # 3. Try to call into cmdline_proc_show(), then SOFT_DISABLED_BIT was
 #    set again!!!
 cat /proc/cmdline

 # 4. Unregister the 'disable_event' command, then:
 #    1) SOFT_DISABLED_BIT was cleared again;
 #    2) trace_buffered_event_disable() was called second time!!!
 echo '!cmdline_proc_show:disable_event:initcall:initcall_finish' > \
     set_ftrace_filter
 ```

To fix it, IIUC, we can change to call trace_buffered_event_enable() at
fist time soft-mode enabled, and call trace_buffered_event_disable() at
last time soft-mode disabled.

Link: https://lore.kernel.org/linux-trace-kernel/20230726095804.920457-1-zhengyejian1@huawei.com

Cc: <mhiramat@kernel.org>
Fixes: 0fc1b09ff1ff ("tracing: Use temp buffer when filtering events")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>