linux-kernel - Re: [PATCH v3 31/35] lib: add memory allocations report in show

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <320cd134-b767-4f29-869b-d219793ba8a1@suse.cz>
Date: Thu, 15 Feb 2024 21:22:07 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
 Suren Baghdasaryan <surenb@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>, akpm@...ux-foundation.org,
 hannes@...xchg.org, roman.gushchin@...ux.dev, mgorman@...e.de,
 dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
 corbet@....net, void@...ifault.com, peterz@...radead.org,
 juri.lelli@...hat.com, catalin.marinas@....com, will@...nel.org,
 arnd@...db.de, tglx@...utronix.de, mingo@...hat.com,
 dave.hansen@...ux.intel.com, x86@...nel.org, peterx@...hat.com,
 david@...hat.com, axboe@...nel.dk, mcgrof@...nel.org, masahiroy@...nel.org,
 nathan@...nel.org, dennis@...nel.org, tj@...nel.org, muchun.song@...ux.dev,
 rppt@...nel.org, paulmck@...nel.org, pasha.tatashin@...een.com,
 yosryahmed@...gle.com, yuzhao@...gle.com, dhowells@...hat.com,
 hughd@...gle.com, andreyknvl@...il.com, keescook@...omium.org,
 ndesaulniers@...gle.com, vvvvvv@...gle.com, gregkh@...uxfoundation.org,
 ebiggers@...gle.com, ytcoode@...il.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 bristot@...hat.com, vschneid@...hat.com, cl@...ux.com, penberg@...nel.org,
 iamjoonsoo.kim@....com, 42.hyeyoo@...il.com, glider@...gle.com,
 elver@...gle.com, dvyukov@...gle.com, shakeelb@...gle.com,
 songmuchun@...edance.com, jbaron@...mai.com, rientjes@...gle.com,
 minchan@...gle.com, kaleshsingh@...gle.com, kernel-team@...roid.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 iommu@...ts.linux.dev, linux-arch@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-modules@...r.kernel.org, kasan-dev@...glegroups.com,
 cgroups@...r.kernel.org
Subject: Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem()

On 2/15/24 19:29, Kent Overstreet wrote:
> On Thu, Feb 15, 2024 at 08:47:59AM -0800, Suren Baghdasaryan wrote:
>> On Thu, Feb 15, 2024 at 8:45 AM Michal Hocko <mhocko@...e.com> wrote:
>> >
>> > On Thu 15-02-24 06:58:42, Suren Baghdasaryan wrote:
>> > > On Thu, Feb 15, 2024 at 1:22 AM Michal Hocko <mhocko@...e.com> wrote:
>> > > >
>> > > > On Mon 12-02-24 13:39:17, Suren Baghdasaryan wrote:
>> > > > [...]
>> > > > > @@ -423,4 +424,18 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
>> > > > >  #ifdef CONFIG_MEMORY_FAILURE
>> > > > >       printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages));
>> > > > >  #endif
>> > > > > +#ifdef CONFIG_MEM_ALLOC_PROFILING
>> > > > > +     {
>> > > > > +             struct seq_buf s;
>> > > > > +             char *buf = kmalloc(4096, GFP_ATOMIC);
>> > > > > +
>> > > > > +             if (buf) {
>> > > > > +                     printk("Memory allocations:\n");
>> > > > > +                     seq_buf_init(&s, buf, 4096);
>> > > > > +                     alloc_tags_show_mem_report(&s);
>> > > > > +                     printk("%s", buf);
>> > > > > +                     kfree(buf);
>> > > > > +             }
>> > > > > +     }
>> > > > > +#endif
>> > > >
>> > > > I am pretty sure I have already objected to this. Memory allocations in
>> > > > the oom path are simply no go unless there is absolutely no other way
>> > > > around that. In this case the buffer could be preallocated.
>> > >
>> > > Good point. We will change this to a smaller buffer allocated on the
>> > > stack and will print records one-by-one. Thanks!
>> >
>> > __show_mem could be called with a very deep call chains. A single
>> > pre-allocated buffer should just do ok.
>> 
>> Ack. Will do.
> 
> No, we're not going to permanently burn 4k here.
> 
> It's completely fine if the allocation fails, there's nothing "unsafe"
> about doing a GFP_ATOMIC allocation here.

Well, I think without __GFP_NOWARN it will cause a warning and thus
recursion into __show_mem(), potentially infinite? Which is of course
trivial to fix, but I'd myself rather sacrifice a bit of memory to get this
potentially very useful output, if I enabled the profiling. The necessary
memory overhead of page_ext and slabobj_ext makes the printing buffer
overhead negligible in comparison?