linux-kernel - [PATCH] mm/slub: Add taint after the errors are printed

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Date:   Wed, 16 Jun 2021 09:25:38 -0700
From:   Georgi Djakov <quic_c_gdjako@...cinc.com>
To:     <vbabka@...e.cz>, <akpm@...ux-foundation.org>,
        <iamjoonsoo.kim@....com>, <rientjes@...gle.com>,
        <penberg@...nel.org>, <cl@...ux.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <djakov@...nel.org>
Subject: [PATCH] mm/slub: Add taint after the errors are printed

When running the kernel with panic_on_taint, the usual slub debug error
messages are not being printed when object corruption happens. That's
because we panic in add_taint(), which is called before printing the
additional information. This is a bit unfortunate as the error messages
are actually very useful, especially before a panic. Let's fix this by
moving add_taint() after the errors are printed on the console.

Signed-off-by: Georgi Djakov <quic_c_gdjako@...cinc.com>
---
 mm/slub.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index a8b0daa1a307..ce7b8e4551b5 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -719,8 +719,6 @@ static void slab_bug(struct kmem_cache *s, char *fmt, ...)
 	pr_err("=============================================================================\n");
 	pr_err("BUG %s (%s): %pV\n", s->name, print_tainted(), &vaf);
 	pr_err("-----------------------------------------------------------------------------\n\n");
-
-	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 	va_end(args);
 }
 
@@ -801,6 +799,7 @@ void object_err(struct kmem_cache *s, struct page *page,
 
 	slab_bug(s, "%s", reason);
 	print_trailer(s, page, object);
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
 static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
@@ -818,6 +817,7 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct page *page,
 	slab_bug(s, "%s", buf);
 	print_page_info(page);
 	dump_stack();
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
 static void init_object(struct kmem_cache *s, void *object, u8 val)
@@ -869,6 +869,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
 					fault, end - 1, fault - addr,
 					fault[0], value);
 	print_trailer(s, page, object);
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
 skip_bug_print:
 	restore_bytes(s, what, value, fault, end);