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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 Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=lHUFofQk; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=OPJCzz5n; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=lHUFofQk; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=OPJCzz5n; dmarc=none; spf=pass (imf19.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Stat-Signature: k5qydgtngfma5bsya1wmb6cpj31wipi1 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C65199001E40 X-HE-Tag: 1623841534-165831 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 6/15/21 5:58 PM, Qian Cai wrote: >=20 >=20 > 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. >>=20 >> To overcome this issues, move the alloc_calls and free_calls >> implementation to debugfs. >>=20 >> Debugfs cache will be created if SLAB_STORE_USER flag is set. >>=20 >> Rename the alloc_calls/free_calls to alloc_traces/free_traces, >> to be inline with what it does. >>=20 >> Reviewed-by: Vlastimil Babka >> Reviewed-by: Greg Kroah-Hartman >> Signed-off-by: Faiyaz Mohammed >=20 > Reverting this commit on today's linux-next fixed all leaks (hundreds) = reported by kmemleak like below, >=20 > 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 >=20 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 =3D v; >> + struct loc_track *t =3D seq->private; >> + >> + if (*ppos < t->count) { >> + *ppos =3D ++*spos; >> + return spos; >> + } >> + *ppos =3D ++*spos; >> + return NULL; >> +} If we return NULL, then NULL is passed to slab_debugfs_stop and thus we d= on'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.