[PATCH 1/3] perf report: Fix OOM error in TUI mode on s390

Thomas Richter
2019-05-22T14:46:28Z

Debugging a OOM error using the TUI interface revealed this issue
on s390:

[tmricht@m83lp54 perf]$ cat /proc/kallsyms |sort
....
00000001119b7158 B radix_tree_node_cachep
00000001119b8000 B __bss_stop
00000001119b8000 B _end
000003ff80002850 t autofs_mount [autofs4]
000003ff80002868 t autofs_show_options [autofs4]
000003ff80002a98 t autofs_evict_inode [autofs4]
....

There is a huge gap between the last kernel symbol
__bss_stop/_end and the first kernel module symbol
autofs_mount (from autofs4 module).

After reading the kernel symbol table via functions:

dso__load()
+--> dso__load_kernel_sym()
+--> dso__load_kallsyms()
+--> __dso_load_kallsyms()
+--> symbols__fixup_end()

the symbol __bss_stop has a start address of 1119b8000 and
an end address of 3ff80002850, as can be seen by this debug statement:

symbols__fixup_end __bss_stop start:0x1119b8000 end:0x3ff80002850

The size of symbol __bss_stop is 0x3fe6e64a850 bytes!
It is the last kernel symbol and fills up the space until
the first kernel module symbol.

This size kills the TUI interface when executing the following
code:

process_sample_event()
hist_entry_iter__add()
hist_iter__report_callback()
hist_entry__inc_addr_samples()
symbol__inc_addr_samples(symbol = __bss_stop)
symbol__cycles_hist()
annotated_source__alloc_histograms(...,
symbol__size(sym),
...)

This function allocates memory to save sample histograms.
The symbol_size() marco is defined as sym->end - sym->start, which
results in above value of 0x3fe6e64a850 bytes and
the call to calloc() in annotated_source__alloc_histograms() fails.

Samples are generated when functions execute.
To fix this I suggest to allow histogram entries only for functions.
Therefore ignore symbol entries which are not of type STT_FUNC.

Output before:
[tmricht@m83lp54 perf]$ ./perf --debug stderr=1 report -vvvvv \
-i ~/slow.data 2>/tmp/2
[tmricht@m83lp54 perf]$ tail -5 /tmp/2
__symbol__inc_addr_samples(875): ENOMEM! sym->name=__bss_stop,
start=0x1119b8000, addr=0x2aa0005eb08, end=0x3ff80002850,
func: 0
problem adding hist entry, skipping event
0x938b8 [0x8]: failed to process type: 68 [Cannot allocate memory]
[tmricht@m83lp54 perf]$

Output after:
[tmricht@m83lp54 perf]$ ./perf --debug stderr=1 report -vvvvv \
-i ~/slow.data 2>/tmp/2
[tmricht@m83lp54 perf]$ tail -5 /tmp/2
symbol__inc_addr_samples map:0x1597830 start:0x110730000 end:0x3ff80002850
symbol__hists notes->src:0x2aa2a70 nr_hists:1
symbol__inc_addr_samples sym:unlink_anon_vmas src:0x2aa2a70
__symbol__inc_addr_samples: addr=0x11094c69e
0x11094c670 unlink_anon_vmas: period++ [addr: 0x11094c69e, 0x2e, evidx=0]
=> nr_samples: 1, period: 526008
[tmricht@m83lp54 perf]$

There is no error about failed memory allocation and the TUI interface
shows all entries.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
---
tools/perf/util/annotate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index 0b8573fd9b05..005cad111586 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -929,7 +929,7 @@ static int symbol__inc_addr_samples(struct symbol *sym, struct map *map,
{
struct annotated_source *src;

- if (sym == NULL)
+ if (sym == NULL || sym->type != STT_FUNC)
return 0;
src = symbol__hists(sym, evsel->evlist->nr_entries);
if (src == NULL)
--
2.19.1