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Fri, 22 Nov 2024 02:48:16 -0800 (PST) MIME-Version: 1.0 References: <20241120102325.3538-1-acarmina@redhat.com> <20241120102602.3e17f2d5@gandalf.local.home> <20241120164043.T1JuBALe@linutronix.de> <20241121170356.eC7f3-1v@linutronix.de> In-Reply-To: <20241121170356.eC7f3-1v@linutronix.de> From: Alessandro Carminati Date: Fri, 22 Nov 2024 11:48:04 +0100 Message-ID: Subject: Re: [PATCH] mm/kmemleak: Fix sleeping function called from invalid context in kmemleak_seq_show To: Sebastian Andrzej Siewior Cc: Steven Rostedt , Catalin Marinas , Andrew Morton , Clark Williams , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Thomas Weissschuh , Alessandro Carminati , Juri Lelli , Gabriele Paoloni , Eric Chanudet X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: rXpi-8AQO6j8cEF530h_ZhMNIx9WlQfo6KORlJb9P1A_1732272496 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D9DB340007 X-Stat-Signature: kpiiukdfidwe9id6usyu611dqbs6qm6s X-Rspam-User: X-HE-Tag: 1732272441-102646 X-HE-Meta: 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 DMNiNvAY AtiRN83jK75ipJt2mjf6wSfmYFB5ywTmyf4XwytE49zyuXNQhwi4FhvyMFAsOjYWGQq/XRGB7LjrJEqstxbwgtNBhn6u8I7dlCkx8C72PhPB8CwEmx1/TqTVwb5sBNlMQApozI4kBGrIuxynR89N3ItsUPfGpr/lWPOGuwFA/zHzAdJcqDWJIoFyQnrAVHZAPv6mAAX0FPyAoJV7n/zaETSDefsI9sO0DmmvpG+X3x89JmGScgt3ljlB8viseczVFRHdZ63guyZ1vSiqLWAq4GYS8AA4A5s8vDJM5YQWr6CvgnE9cZbL3XMki2fYiZEgS8TwjEGc3L5VvbNEIMnAbl0Q5/0nMruUkn+Vlj/fl/Inugt016fHeVIBp1g== 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: List-Subscribe: List-Unsubscribe: Hi Sebastian, On Thu, Nov 21, 2024 at 6:04=E2=80=AFPM Sebastian Andrzej Siewior wrote: > > On 2024-11-21 17:50:06 [+0100], Alessandro Carminati wrote: > > Hello Sebastian, > Hi Alessandro, > > > On Wed, Nov 20, 2024 at 5:40=E2=80=AFPM Sebastian Andrzej Siewior > > wrote: > > > > > > On 2024-11-20 10:26:02 [-0500], Steven Rostedt wrote: > > > > The "%pK" dereferences a pointer and there's some SELinux hooks att= ached to > > > > that code. The problem is that the SELinux hooks take spinlocks. Th= is would > > > > not have been an issue if it wasn't for that "%pK" in the format. > > > > > > That is missing check and I think Thomas Weissschuh wanted to add it.= So > > > we don't call into selinux. > > > > Your comment confuses me a bit, as I'm unsure what Thomas is actually > > working on. > > Am I correct in assuming he's addressing a fix in lib/vsprintf.c to ens= ure > > that sleeping functions aren't called, allowing these functions to work= in > > any context? > > restricted_pointer() has a check for in_hardirq() among others. This > needs an additional PREEMPT_RT check. > I would be actual in favour to get rid of case 1 for kptr_restrict and > have either 0 or 2. > > > However, his mention of "This fix for kmemleak is still needed as the > > pointers in the kmemleak report are useful" adds to my confusion. > > Meanwhile, Steven suggests reworking SELinux to resolve the issue. > > Could you clarify what you mean by "So we don't call into selinux"? > > This getting out of hand. By adding the PREEMPT_RT check to > restricted_pointer() we don't call in selinux so the problem is gone. I am really glad that now we have a clear solution, however practically speaking is Thomas working on such a patch or is he working on something related that does not fully solve the problem? Even if he is working on a partial solution, I am happy to coordinate off-list working on his own private branch (or else I would just give up and review the Thomas' patchset when it is out...) > kmemleak is not the only problem. printk(), as another of vspritf pointer > code user, can be called from any place and would also trigger a > warning here. > As far as "kmemleak need to be usefull" goes: With kptr_restrict =3D=3D 0 > then with or without pointer hashing they will be useful. If we need to > go via selinux then it ends as a hint. > > Sebastian > --=20 --- 172