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b=h2fUmmAw08Qwd7I9H/YkS6V49OVT9cnwKs2ul0tRBzEVbsIIzHzcEZI5VmE2sQwPK evshluf+HwhFM/S7LAg02cB0gfchFnW9Xomf4eSdo37ph8cKMumr2cq7SUqFG6WsE5 kgk/+mad9S5QkOz+1PYKWO5DImEkSTZ7J09KQ7icUugX/7oGr2+uJ0u9YdYZH02/Yq rueOzDq5GphY6gWk+bvl7RZWgRge5k40vqrLjye/V51/NF+/B4UQ9AS8JVeu6dcUmE Ay3awib8Z3YndRRjjnFwFyx5sxQ6L7LJpSfMwGt6Q9HqsG5lW/1jdj5KfJwgRc5tld WhqgSunWu0Swg== From: SeongJae Park To: SeongJae Park Cc: damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [RFC PATCH v5 04/11] mm/damon/sysfs-schemes: implement fail_charge_{num,denom} files Date: Fri, 10 Apr 2026 16:58:18 -0700 Message-ID: <20260410235819.91133-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260410142034.83798-5-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B45231C0005 X-Stat-Signature: g1cayrbgcw8djnaqpngm5fd46u5jzuq7 X-Rspam-User: X-HE-Tag: 1775865502-726590 X-HE-Meta: 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 fvYC3GVQ HmncnkI7zztsLOl/O4RuVGdiuDBKmIkwZBBsumX1Q4M1F0atX0Ag/JMVhg/ZzMvWK7ApVEQvRPsr78iRQJ+Q2EUQ0UotpNa5g4lBMewrgLpdicK+E3pVRmiqZuPuhuhqXuJxEY0CU2/VFfTf5BO463Uy7Hyw4NcXazmlpM7mSAe2WQBSiL++0DgpE+kq5+0wqx0oJnvTIZWROT6qolSMEuqMioXbbdOrGMbG2KCgwyE4/BXylzo5mb0FkwZqQ4zHZjSOgZVbEGKTyWwfhCuiTr7WcLwWnAfWWOoGg+cSv/O1owK36hjSVZ6YqPFvJD5Jg7ZUsTCEQUySy0f/ntDtfPOkiOK87tBC9AB/pzMag/nr3MQCKk2/X9VioK4WY86bzUNaaJpj1j0zhlSVU433x3QWBXWAxBIwrcCbJPb/EyyqBH4U= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: TL; DR: sashiko asking a question that was raised on the previous version and I decided to ignore. My opinion is still same. Forwarding sashiko review in a reply format with my inline comments below, for details of my view and doing discussions via mails if needed. > # review url: https://sashiko.dev/#/patchset/20260410142034.83798-5-sj@kernel.org > # start of sashiko.dev inline review > commit efc09e724c58ae44645ba20d1865e976eae67242 > Author: SeongJae Park > > mm/damon/sysfs-schemes: implement fail_charge_{num,denom} files > > This commit implements the user-space ABI for the DAMOS action failed region > quota-charge ratio setup. It adds fail_charge_num and fail_charge_denom > sysfs files for reading and setting the numerator and denominator of the > failed regions charge ratio. > > > diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c > > index 5186966dafb35..d5bfba79f105f 100644 > > --- a/mm/damon/sysfs-schemes.c > > +++ b/mm/damon/sysfs-schemes.c > > [ ... ] > > > @@ -1663,6 +1665,48 @@ static ssize_t goal_tuner_store(struct kobject *kobj, > > return -EINVAL; > > } > > > > +static ssize_t fail_charge_num_show(struct kobject *kobj, > > + struct kobj_attribute *attr, char *buf) > > +{ > > + struct damon_sysfs_quotas *quotas = container_of(kobj, > > + struct damon_sysfs_quotas, kobj); > > + > > + return sysfs_emit(buf, "%u\n", quotas->fail_charge_num); > > +} > > + > > +static ssize_t fail_charge_num_store(struct kobject *kobj, > > + struct kobj_attribute *attr, const char *buf, size_t count) > > +{ > > + struct damon_sysfs_quotas *quotas = container_of(kobj, > > + struct damon_sysfs_quotas, kobj); > > + int err = kstrtouint(buf, 0, "as->fail_charge_num); > > Could unbounded values set here cause an integer overflow in > damos_charge_quota() on 32-bit architectures? > > Because kstrtouint() allows values up to UINT_MAX, fail_charge_num and > fail_charge_denom can be quite large. When these are used in mult_frac() > for calculating the fractional charge: > > mult_frac((sz_region - sz_applied), quota->fail_charge_num, > quota->fail_charge_denom) > > The mult_frac(x, n, d) macro computes (x / d) * n + (x % d) * n / d, where > the types are determined by typeof(x). Here x is an unsigned long. > > If userspace provides large values like 1,000,000 for both the numerator > and denominator, the remainder (x % d) can be up to 999,999. The > intermediate multiplication (x % d) * n could be around 10^11, which would > silently overflow ULONG_MAX on 32-bit systems. > > Is this potential integer overflow a regression that results in an incorrectly > small fractional charge, causing DAMON to under-charge the quota limit and > bypass the configured scheme quotas? > > > # end of sashiko.dev inline review > # review url: https://sashiko.dev/#/patchset/20260410142034.83798-5-sj@kernel.org Thanks, SJ # hkml [1] generated a draft of this mail. You can regenerate # this using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260410142034.83798-5-sj@kernel.org # # [1] https://github.com/sjp38/hackermail