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Tengda Wu e80ff23ba8 ftrace: Fix potential warning in trace_printk_seq during ftrace_dump 
[ Upstream commit 4013aef2ce ]

When calling ftrace_dump_one() concurrently with reading trace_pipe,
a WARN_ON_ONCE() in trace_printk_seq() can be triggered due to a race
condition.

The issue occurs because:

CPU0 (ftrace_dump)                              CPU1 (reader)
echo z > /proc/sysrq-trigger

!trace_empty(&iter)
trace_iterator_reset(&iter) <- len = size = 0
                                                cat /sys/kernel/tracing/trace_pipe
trace_find_next_entry_inc(&iter)
  __find_next_entry
    ring_buffer_empty_cpu <- all empty
  return NULL

trace_printk_seq(&iter.seq)
  WARN_ON_ONCE(s->seq.len >= s->seq.size)

In the context between trace_empty() and trace_find_next_entry_inc()
during ftrace_dump, the ring buffer data was consumed by other readers.
This caused trace_find_next_entry_inc to return NULL, failing to populate
`iter.seq`. At this point, due to the prior trace_iterator_reset, both
`iter.seq.len` and `iter.seq.size` were set to 0. Since they are equal,
the WARN_ON_ONCE condition is triggered.

Move the trace_printk_seq() into the if block that checks to make sure the
return value of trace_find_next_entry_inc() is non-NULL in
ftrace_dump_one(), ensuring the 'iter.seq' is properly populated before
subsequent operations.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ingo Molnar <mingo@elte.hu>
Link: https://lore.kernel.org/20250822033343.3000289-1-wutengda@huaweicloud.com
Fixes: d769041f86 ("ring_buffer: implement new locking")
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-09-04 15:26:24 +02:00
arch mips: lantiq: xway: sysctrl: rename the etop node 2025-09-04 15:26:24 +02:00
block
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Documentation bonding: Add independent control state machine 2025-08-28 16:26:18 +02:00
drivers pinctrl: STMFX: add missing HAS_IOMEM dependency 2025-09-04 15:26:24 +02:00
fs alloc_fdtable(): change calling conventions. 2025-08-28 16:26:19 +02:00
include bonding: Add independent control state machine 2025-08-28 16:26:18 +02:00
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kernel ftrace: Fix potential warning in trace_printk_seq during ftrace_dump 2025-09-04 15:26:24 +02:00
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sound ALSA: usb-audio: Use correct sub-type for UAC3 feature unit validation 2025-08-28 16:26:18 +02:00
tools bonding: Add independent control state machine 2025-08-28 16:26:18 +02:00
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Makefile Linux 6.1.149 2025-08-28 16:26:19 +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.