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

[Arnaldo Carvalho de Melo]

On Wed, Jan 08, 2025 at 06:06:03PM +0100, Christophe Leroy wrote:
> 
> 
> 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));
> +	}

Its ok, I'll keep it now that I looked at it.

Thanks!

- Arnaldo