From 89bab1dba8a0167ef0d819e0f55b6bafa038e87f Mon Sep 17 00:00:00 2001 From: Krystian Kaniewski Date: Thu, 24 Sep 2026 10:49:42 +0200 Subject: [PATCH] ring-buffer: Fix false warning in ring_buffer_map_get_reader() The mmap reader can warn when it catches up with a writer that is still committing events. rb_get_reader_page() returns NULL in this case, but ring_buffer_map_get_reader() treats that result as an error. The initial rb_per_cpu_empty() check filters out an empty buffer, but it does not guarantee that the next reader page has committed data. Writers do not take reader_lock and can advance commit_page before publishing the committed length on the new page. rb_get_reader_page() can swap to that page, catch up with the writer and return NULL. Handle NULL through the existing no-data exit without warning. Remove the caller's reader_page == commit_page check as well, since the reader-page helper already handles that case. The existing metadata update and return path remain in place. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260924084946.20104-1-krystianmkaniewski@gmail.com Fixes: 117c39200d9d ("ring-buffer: Introducing ring-buffer mapping functions") Assisted-by: Gemini:gemini-3.8-flash syzbot Reported-by: syzbot+de3d7f9bcc9212f3fae1@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=de3d7f9bcc9212f3fae1 Link: https://syzkaller.appspot.com/ai_job?id=488adc18-a10e-42d2-a205-25327c38837f Signed-off-by: Krystian Kaniewski Reviewed-by: Vincent Donnefort Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index ad3bc48e2670..e2b721d0707f 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7998,12 +7998,8 @@ consume: goto out; } - /* Did the reader catch up with the writer? */ - if (cpu_buffer->reader_page == cpu_buffer->commit_page) - goto out; - reader = rb_get_reader_page(cpu_buffer); - if (WARN_ON(!reader)) + if (!reader) goto out; /* Check if any events were dropped */