[PATCH OLK-6.6 0/2] Fix ringbuffer swap cpu buffer issue
This series backports two mainline patches to resolve an issue with swapping CPU buffers in the ring buffer. Steven Rostedt (1): ring-buffer: Remove jump to out label in ring_buffer_swap_cpu() Tengda Wu (1): ring-buffer: Use current_context for safe per-CPU buffer swap kernel/trace/ring_buffer.c | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-) -- 2.34.1
From: Steven Rostedt <rostedt@goodmis.org> mainline inclusion from mainline-v6.16-rc1 commit f115d2b70bff2665f67fa8e8dc5ed9452b696c44 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 function ring_buffer_swap_cpu() has a bunch of jumps to the label out that simply returns "ret". There's no reason to jump to a label that simply returns a value. Just return directly from there. This goes back to almost the beginning when commit 8aabee573dff ("ring-buffer: remove unneeded get_online_cpus") was introduced. That commit removed a put_online_cpus() from that label, but never updated all the jumps to it that now no longer needed to do anything but return a value. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Link: https://lore.kernel.org/20250527145753.6b45d840@gandalf.local.home Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Conflicts: kernel/trace/ring_buffer.c [Context conflict] Signed-off-by: Tengda Wu <wutengda2@huawei.com> --- kernel/trace/ring_buffer.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3b42f1632cda..e8432244f2c6 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5480,28 +5480,26 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, if (!cpumask_test_cpu(cpu, buffer_a->cpumask) || !cpumask_test_cpu(cpu, buffer_b->cpumask)) - goto out; + return -EINVAL; cpu_buffer_a = buffer_a->buffers[cpu]; cpu_buffer_b = buffer_b->buffers[cpu]; /* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages) - goto out; - - ret = -EAGAIN; + return -EINVAL; if (atomic_read(&buffer_a->record_disabled)) - goto out; + return -EAGAIN; if (atomic_read(&buffer_b->record_disabled)) - goto out; + return -EAGAIN; if (atomic_read(&cpu_buffer_a->record_disabled)) - goto out; + return -EAGAIN; if (atomic_read(&cpu_buffer_b->record_disabled)) - goto out; + return -EAGAIN; /* * We can't do a synchronize_rcu here because this @@ -5538,7 +5536,6 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, out_dec: atomic_dec(&cpu_buffer_a->record_disabled); atomic_dec(&cpu_buffer_b->record_disabled); -out: return ret; } EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu); -- 2.34.1
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 e8432244f2c6..50015d7479f9 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)) @@ -5510,10 +5510,10 @@ 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
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