Re: [PATCH v2] perf: Fix display of kernel symbols

[Christophe Leroy]

Le 08/01/2025 à 15:53, Arnaldo Carvalho de Melo a écrit :
> On Wed, Jan 08, 2025 at 10:54:20AM +0100, Christophe Leroy wrote:
> > Since commit 659ad3492b91 ("perf maps: Switch from rbtree to lazily
> > sorted array for addresses"), perf doesn't display anymore kernel
> > symbols on powerpc, allthough it still detects them as kernel addresses.
> >
> > 	# Overhead  Command     Shared Object  Symbol
> > 	# ........  ..........  ............. ......................................
> > 	#
> > 	    80.49%  Coeur main  [unknown]      [k] 0xc005f0f8
> > 	     3.91%  Coeur main  gau            [.] engine_loop.constprop.0.isra.0
> > 	     1.72%  Coeur main  [unknown]      [k] 0xc005f11c
> > 	     1.09%  Coeur main  [unknown]      [k] 0xc01f82c8
> > 	     0.44%  Coeur main  libc.so.6      [.] epoll_wait
> > 	     0.38%  Coeur main  [unknown]      [k] 0xc0011718
> > 	     0.36%  Coeur main  [unknown]      [k] 0xc01f45c0
> >
> > This is because function maps__find_next_entry() now returns current
> > entry instead of next entry, leading to kernel map end address
> > getting mis-configured with its own start address instead of the
> > start address of the following map.
> >
> > Fix it by really taking the next entry, also make sure that entry
> > follows current one by making sure entries are sorted.
> >
> > Fixes: 659ad3492b91 ("perf maps: Switch from rbtree to lazily sorted array for addresses")
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > Reviewed-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > ---
> > v2: Make sure the entries are sorted, if not sort them.
>
> Since you have changed what I reviewed I'll have to re-review :-) Will
> try to do it after some calls.

Ah yes sorry, should have removed your Reviewed-by.

Based on Ian's feedback "Using the next entry in this way won't work if 
the entries aren't sorted", I added the following block in front of the 
initial change:

+	while (!maps__maps_by_address_sorted(maps)) {
+		up_read(maps__lock(maps));
+		maps__sort_by_address(maps);
+		down_read(maps__lock(maps));
+	}

Christophe