From: Brian Foster <bfoster@redhat.com>
To: linux-bcachefs@vger.kernel.org
Subject: [BUG] trace_printk() broken?
Date: Mon, 12 Dec 2022 14:20:39 -0500 [thread overview]
Message-ID: <Y5d/B88BOu6qOE5X@bfoster> (raw)
Hi,
While poking around the bcachefs tree I ran into a problem where
trace_printk() seems to be broken. I suspect this has something to do
with the printbuf bits as it works once I back out some of those
changes.
What I observe is that a smaller printk with a fixed string seems to
work as expected, but once I add some variable args the message string
seems to get chewed up. This results in wonky formatting when reading
/sys/kernel/debug/tracing/trace and a read of the corresponding
trace_pipe file seems to spin in a livelock.
A diff is appended below to give a simple example of each case. A read
of the trace file ends up looking like this:
fsck.ext4-535 [003] ..... 6.112680: write_cache_pages: fsck.ext4-535 [003] ..... 6.113224: write_cache_pages: test
fsck.ext4-535 [003] ..... 6.117957: write_cache_pages: fsck.ext4-535 [003] ..... 6.118445: write_cache_pages: test
...
Brian
--- 8< ---
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 032a7bf8d259..59ae76cb5756 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2355,6 +2355,9 @@ int write_cache_pages(struct address_space *mapping,
if (!clear_page_dirty_for_io(page))
goto continue_unlock;
+ trace_printk("%d: ino 0x%lx\n", __LINE__, mapping->host->i_ino);
+ trace_printk("test\n");
+
trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
error = (*writepage)(page, wbc, data);
if (unlikely(error)) {
next reply other threads:[~2022-12-12 19:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-12 19:20 Brian Foster [this message]
2022-12-13 23:32 ` [BUG] trace_printk() broken? Kent Overstreet
2022-12-14 17:46 ` Brian Foster
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