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b=lqXFDyDV9otA+OWWxyegWyB2sC0/phLyMCIu69a/z/18CcyyzQHkRiRwLNAU4uT9x UHmK7u7+y6j1MNI/A2UQAN4HdnMDn8tCIO3z2TvFbK4XPsMn0aF+kZOlGS810H+alZ oMI2C8UdG5ZSu1ET+OgQwZvDc8zZz+pZh9C9xwePCd/4hCJhqLtsmEOOCMVd0V4o9Y x2lA6i6eCj0auShuv8ePOU+93xYhtm50RIIRHSDdX4M+7f2YjPok+TRGUXUtIFfcve MIX548aVJMghxoE/I2gJz4+uUST8UZSgeeA0+laDNPVOk+Ceoe/W8N3NMlefqlC8jO 263bKfaqOVWqg== From: SJ Park To: sashiko-bot@kernel.org Cc: SJ Park , "Andrew Morton" , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [RFC PATCH 6.1.y 2/2] mm/damon/core: remove unreachable damos charge_{target,addr}_from Date: Sat, 7 Nov 2026 15:04:04 -0800 Message-ID: <20261107230406.340832-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: q4wy36d8tagb4566f8d7osh8p3sz6dgq X-Rspamd-Queue-Id: 967681C0009 X-Rspam-User: X-HE-Tag: 1794092653-936541 X-HE-Meta: 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 e7VS9XiT i2+sOcN3Z0UvjTcMjnBLfrvQc1WJePA5bf9k2gPztyjRkoHkvPQnaQ4AXXjYMH84JHmJRUGXHmtBCuiZjKgpoFPtqSfRC/xYEMNdlkLyspyu+U3Ej00HEPe2VMCGQucd1AgcsMZlQ+hWPqm7Nu67bqGUnmHUh8TMalWgge3APEr7OktvD9GjOB0r0u3fccImrrViTKZ+b3sSPUMB9QlMwnP/oWqSRCqBiNUga9VEqcHlNnCIh9x2tMFNXQIU3B6VNVBnPMOEd/m+fvang48k7Nv6lNAB1Vq7jlK49niQOKkToNps95ixdy6FU1nM7gcTY0v0Kl4EZ3PjGJoz71gMsEBgGDzOfkTIFAVx+68VPY2lS/KuKvjt/8PLP1w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sat, 07 Nov 2026 23:02:33 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential > issue to consider: > - [Medium] mm/damon/core: stale charge_target_from ABA reuse when scheme > is inactive > -- > > commit 853b3e89da132f2ce03750bcf6dfc1f62a70d261 > Author: SJ Park > > mm/damon/core: remove unreachable damos charge_{target,addr}_from > > This commit adds damos_fix_stale_charge_pointers() to clear > quota->charge_target_from and quota->charge_addr_from when the referenced > target has been removed or no longer has any regions. > > Link: https://lore.kernel.org/20261020023958.108276-1-sj@kernel.org > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index 9206737d05ae7..01f93146b92fe 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > @@ -860,6 +860,26 @@ static void damos_set_effective_quota(struct damos_quota *quota) > > quota->esz = esz; > > } > > > > +static void damos_fix_stale_charge_pointers(struct damon_ctx *c, > > + struct damos *s) > > +{ > > + struct damos_quota *quota; > > + struct damon_target *t; > > + > > + quota = &s->quota; > > + if (!quota->charge_target_from) > > + return; > > + damon_for_each_target(t, c) { > > + if (t == quota->charge_target_from) { > > + if (damon_nr_regions(t) > 0) > > + return; > > + break; > > + } > > + } > > + quota->charge_target_from = NULL; > > + quota->charge_addr_from = 0; > > +} > > + > > static void kdamond_apply_schemes(struct damon_ctx *c) > > { > > struct damon_target *t; > > @@ -890,6 +910,8 @@ static void kdamond_apply_schemes(struct damon_ctx *c) > > damos_set_effective_quota(quota); > > } > > > > + damos_fix_stale_charge_pointers(c, s); > > + > > if (!c->ops.get_scheme_score) > > continue; > > > > [Severity: Medium] > Can quota->charge_target_from match a newly allocated target due to slab > address reuse if the old target was freed while the scheme was inactive? > > kdamond_apply_schemes() skips inactive schemes at the !s->wmarks.activated > check before reaching damos_fix_stale_charge_pointers(), and > damon_sysfs_set_targets() frees removed targets via damon_destroy_target() > without clearing charge_target_from. If an online commit removes the > target stored in charge_target_from while the scheme is deactivated by > watermarks and a later commit allocates a new target at the same address, > damos_fix_stale_charge_pointers() will see t == quota->charge_target_from > with regions present and leave the stale charge_target_from and > charge_addr_from in place. When the scheme reactivates, > damon_do_apply_schemes() will skip targets before the new target and > regions up to the old charge_addr_from. Good finding but no real issue. Occasionally starting quota charging from an unexpected target is no real issue for DAMOS in my opinion. So, no blocker. > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/20261107224800.340250-1-sj@kernel.org?part=2 > Thanks, SJ