From: Tengda Wu <wutengda@huaweicloud.com> mainline inclusion from mainline-v7.2-rc7 commit f27bdc43077e4fcb5557dfc315ee8d91e741f483 category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/9717 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- The ring_buffer_swap_cpu() function currently checks the per-CPU committing counter to determine if a buffer is actively being written to before performing the swap. However, there exists a race window where this check can be bypassed: ring_buffer_lock_reserve cpu_buffer = buffer->buffers[cpu]; // cpu_buffer_a rb_reserve_next_event rb_start_commit // inc committing if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {...} __rb_reserve_next rb_move_tail rb_end_commit(cpu_buffer); // dec committing => 0 /* interrupt hits here, successfully swaps! */ local_inc(&cpu_buffer->committing); ring_buffer_unlock_commit cpu_buffer = buffer->buffers[cpu]; // cpu_buffer_b rb_commit rb_end_commit RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing)) // triggers warning The committing counter can temporarily drop to 0 during a single write operation (within rb_move_tail), creating a window where swap can succeed even though the write is still in progress. This leads to inconsistent buffer state and triggers the RB_WARN_ON in rb_commit(). Replace the committing counter check with current_context checks, which are set at the entry of ring_buffer_lock_reserve() and remain valid throughout the entire write operation, providing a reliable indicator of buffer busy state during swap. Cc: stable@vger.kernel.org Fixes: 4239c38fe0b3 ("ring-buffer: Process commits whenever moving to a new page.") Link: https://patch.msgid.link/20260803005640.2445666-2-wutengda@huaweicloud.com Signed-off-by: Tengda Wu <wutengda@huaweicloud.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Tengda Wu <wutengda2@huawei.com> --- kernel/trace/ring_buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3b42f1632cda..52e6ccb68067 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5476,7 +5476,7 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, { struct ring_buffer_per_cpu *cpu_buffer_a; struct ring_buffer_per_cpu *cpu_buffer_b; - int ret = -EINVAL; + int ret = -EBUSY; if (!cpumask_test_cpu(cpu, buffer_a->cpumask) || !cpumask_test_cpu(cpu, buffer_b->cpumask)) @@ -5512,10 +5512,10 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, atomic_inc(&cpu_buffer_a->record_disabled); atomic_inc(&cpu_buffer_b->record_disabled); - ret = -EBUSY; - if (local_read(&cpu_buffer_a->committing)) + /* Do not swap if either buffer is in the process of writing */ + if (cpu_buffer_a->current_context) goto out_dec; - if (local_read(&cpu_buffer_b->committing)) + if (cpu_buffer_b->current_context) goto out_dec; /* -- 2.34.1