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bh=hcnqgYV1OHaJr0sq4rpPF6e//e/o64rPvF0s7j9YdWo=; b=OPJCzz5nh9hmVzow8cUb64+csDdolPJFKZYD24Z8N/xvAkA8HEvSonlpWmcUOYggqUVed1 d07OTbm8iBqpfbBA== Received: from director2.suse.de ([192.168.254.72]) by imap3-int with ESMTPSA id QtwCGQnbyWDBYgAALh3uQQ (envelope-from ); Wed, 16 Jun 2021 11:05:45 +0000 To: Qian Cai , Faiyaz Mohammed , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, greg@kroah.com, glittao@gmail.com, andy.shevchenko@gmail.com Cc: vinmenon@codeaurora.org, Catalin Marinas References: <1623438200-19361-1-git-send-email-faiyazm@codeaurora.org> <8c821abf-8fa6-b78b-cea4-b7d3b3b74a69@quicinc.com> From: Vlastimil Babka Subject: Re: [PATCH v12] mm: slub: move sysfs slab alloc/free interfaces to debugfs Message-ID: Date: Wed, 16 Jun 2021 13:05:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <8c821abf-8fa6-b78b-cea4-b7d3b3b74a69@quicinc.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/15/21 5:58 PM, Qian Cai wrote: > > > On 6/11/2021 3:03 PM, Faiyaz Mohammed wrote: >> alloc_calls and free_calls implementation in sysfs have two issues, >> one is PAGE_SIZE limitation of sysfs and other is it does not adhere >> to "one value per file" rule. >> >> To overcome this issues, move the alloc_calls and free_calls >> implementation to debugfs. >> >> Debugfs cache will be created if SLAB_STORE_USER flag is set. >> >> Rename the alloc_calls/free_calls to alloc_traces/free_traces, >> to be inline with what it does. >> >> Reviewed-by: Vlastimil Babka >> Reviewed-by: Greg Kroah-Hartman >> Signed-off-by: Faiyaz Mohammed > > Reverting this commit on today's linux-next fixed all leaks (hundreds) reported by kmemleak like below, > > unreferenced object 0xffff00091ae1b540 (size 64): > comm "lsbug", pid 1607, jiffies 4294958291 (age 1476.340s) > hex dump (first 32 bytes): > 02 00 00 00 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b ........kkkkkkkk > 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk > backtrace: > [] slab_post_alloc_hook+0xa0/0x418 > [] kmem_cache_alloc_trace+0x1e4/0x378 > [] slab_debugfs_start+0x30/0x50 > slab_debugfs_start at /usr/src/linux-next/mm/slub.c:5831 > [] seq_read_iter+0x214/0xd50 > [] seq_read+0x28c/0x418 > [] full_proxy_read+0xdc/0x148 > [] vfs_read+0x104/0x340 > [] ksys_read+0xf8/0x1e0 > [] __arm64_sys_read+0x74/0xa8 > [] invoke_syscall.constprop.0+0xdc/0x1d8 > [] do_el0_svc+0xe4/0x298 > [] el0_svc+0x20/0x30 > [] el0t_64_sync_handler+0xb0/0xb8 > [] el0t_64_sync+0x178/0x17c > I think the problem is here: >> +static void slab_debugfs_stop(struct seq_file *seq, void *v) >> +{ >> + kfree(v); >> +} >> + >> +static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos) >> +{ >> + loff_t *spos = v; >> + struct loc_track *t = seq->private; >> + >> + if (*ppos < t->count) { >> + *ppos = ++*spos; >> + return spos; >> + } >> + *ppos = ++*spos; >> + return NULL; >> +} If we return NULL, then NULL is passed to slab_debugfs_stop and thus we don't kfree ppos. kfree(NULL) is silently ignored. I think as we have private struct loc_track, we can add a pos field there and avoid the kmaloc/kfree altogether.