For some reason, this email did not make it to linux-trace-kernel@vger.kernel.org, and therefore did not make it into patchwork?
John?
-- Steve
On Wed, 26 Apr 2023 09:04:44 +0800 Tze-nan.Wu Tze-nan.Wu@mediatek.com wrote:
From: "Tze-nan Wu" Tze-nan.Wu@mediatek.com
In ring_buffer_reset_online_cpus, the buffer_size_kb write operation may permanently fail if the cpu_online_mask changes between two for_each_online_buffer_cpu loops. The number of increases and decreases on both cpu_buffer->resize_disabled and cpu_buffer->record_disabled may be inconsistent, causing some CPUs to have non-zero values for these atomic variables after the function returns.
This issue can be reproduced by "echo 0 > trace" while hotplugging cpu. After reproducing success, we can find out buffer_size_kb will not be functional anymore.
To prevent leaving 'resize_disabled' and 'record_disabled' non-zero after ring_buffer_reset_online_cpus returns, we ensure that each atomic variable has been set up before atomic_sub() to it.
Cc: stable@vger.kernel.org Cc: npiggin@gmail.com Fixes: b23d7a5f4a07 ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU") Reviewed-by: Cheng-Jui Wang cheng-jui.wang@mediatek.com Signed-off-by: Tze-nan Wu Tze-nan.Wu@mediatek.com
Changes from v4 to v5: https://lore.kernel.org/lkml/20230412112401.25081-1-Tze-nan.Wu@mediatek.com/
- Move the define before the function
kernel/trace/ring_buffer.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 76a2d91eecad..253ef85a9ec3 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5345,6 +5345,9 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu) } EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu); +/* Flag to ensure proper resetting of atomic variables */ +#define RESET_BIT (1 << 30)
/**
- ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer
- @buffer: The ring buffer to reset a per cpu buffer of
@@ -5361,20 +5364,27 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer) for_each_online_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->resize_disabled);
atomic_add(RESET_BIT, &cpu_buffer->resize_disabled);/* Make sure all commits have finished */ synchronize_rcu();
- for_each_online_buffer_cpu(buffer, cpu) {
- for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu];
/** If a CPU came online during the synchronize_rcu(), then* ignore it.*/if (!(atomic_read(&cpu_buffer->resize_disabled) & RESET_BIT))continue;- reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);mutex_unlock(&buffer->mutex);