Re: [PATCH 06/14] md/bcache: Use %pS printk format for direct addresses

On 07.09.2017 06:50, Coly Li wrote:

On 2017/9/7 上午4:27, Helge Deller wrote:

quoted

Use the %pS instead of the %pF printk format specifier for printing symbols
from direct addresses. This is needed for the ia64, ppc64 and parisc64
architectures.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: linux-bcache@vger.kernel.org
Cc: linux-raid@vger.kernel.org
---
 drivers/md/bcache/closure.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/closure.c b/drivers/md/bcache/closure.c
index 864e673..0b0c9bc 100644
--- a/drivers/md/bcache/closure.c
+++ b/drivers/md/bcache/closure.c

@@ -175,7 +175,7 @@ static int debug_seq_show(struct seq_file *f, void *data)
 	list_for_each_entry(cl, &closure_list, all) {
 		int r = atomic_read(&cl->remaining);
 
-		seq_printf(f, "%p: %pF -> %pf p %p r %i ",
+		seq_printf(f, "%p: %pS -> %pf p %p r %i ",
 			   cl, (void *) cl->ip, cl->fn, cl->parent,
 			   r & CLOSURE_REMAINING_MASK);
 

@@ -187,7 +187,7 @@ static int debug_seq_show(struct seq_file *f, void *data)
 			   r & CLOSURE_SLEEPING	? "Sl" : "");
 
 		if (r & CLOSURE_WAITING)
-			seq_printf(f, " W %pF\n",
+			seq_printf(f, " W %pS\n",
 				   (void *) cl->waiting_on);
 
 		seq_printf(f, "\n");

It is unclear to me, that if %pF is used, on ia64/ppc64/parisc64 a
function descriptor conversion happens, what negative effect exactly
takes place ?

On ia64/ppc64/parisc64 the kernel will crash here in the worst case, because
vsprintf() will try to read a pointer from that address and resolve it. 
But you hand over a return address (_RET_IP_) which should be 
resolved directly to a symbol. For that you need to use the %pS specifier,
which is what my patch does.

The patch has no negative effect on any platform. Output will still be the
same on x86/mips/arm/... as it has been before with %pF. The only positive
effect of the patch is that the seq_printf will now show correct output on 
ia64/ppc64/parisc64 too.

Helge