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b=eq8LOAv38/JT//HvNVNFuX9mQYVns/QjBaRg4lFD6H13iiyHwdAqqGAHzowFBfpYp TQ845vSB2U/vzHnithCWeTxZHU2L4LlQ+w4ohRPsP+z26/uQkgXKJqxWwF7prLpa7F v8OfWijkA7lDe0BKpuxMaLmjq7HPpxf92RN3DuqjlxcCn3NT+Gu63ScjWp2C/hdYEC BJjrA9WqF1RvbnR5DP1QYEhLqbnKaftOrbc1Bb/x/+npMXPDZCH0OFnE1Yr2GL2PBB Dz3LKLleFAI+dUaGDHW7S0oF1Y/p+03h9hzlCS7svr+6fURFqcY4prI2uxh8l5Thdc Ihs5v09i67MxA== From: SJ Park To: Cc: SJ Park , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH 5/5] mm/damon/sysfs: read ops_id only once Date: Sat, 11 Jul 2026 11:04:08 -0700 Message-ID: <20260711180409.82093-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260711180409.82093-1-sj@kernel.org> References: <20260711180409.82093-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 855BEC0004 X-Stat-Signature: w3hoiz8mqj9c1t48u46uiy8yjkko48pc X-HE-Tag: 1783793062-318179 X-HE-Meta: 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 mjpMbtky anbDtbSwQzdjQ6TF9Sxt86wS4+evQsV+cLMA3jUes4IFZOWo+OATsaBF5I3obLVhZIHo1+bn3m2RBcl5WbHyIKSWyqB5Ut1PV2gv72tBotOYZcV6vYcEhXzakxLA4ZHhHU5bHIaxZerYai32tnajn5Ys0kQNfanTwRByZWq7OC78ldtGnc9DeMQM1+N9gVdydWeYxobwFojJYu/XZC60b/g67KjPlokBABm8pvbwahdxgFga3INkHrEBR19ndv1AnSVoxGdMtPu/Fa9BlfzQ68ifHXw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_sysfs_apply_inputs() reads ops_id twice. It could race with ops_id_store(). As a result, the min_region_sz could wrongly be set up. Read it once. The user impact is trivial. Sane users ain't update the parameter in parallel. Even if it happens, only monitoring itself runs differently than expected. No critical consequences like kernel panic or memory corruption happen. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260703172417.95426-1-sj@kernel.org Signed-off-by: SJ Park --- mm/damon/sysfs.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index b5fe036f78015..60a1a9e4ada34 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -2094,14 +2094,16 @@ static inline bool damon_sysfs_kdamond_running( static int damon_sysfs_apply_inputs(struct damon_ctx *ctx, struct damon_sysfs_context *sys_ctx) { + enum damon_ops_id ops_id; int err; - err = damon_select_ops(ctx, sys_ctx->ops_id); + ops_id = READ_ONCE(sys_ctx->ops_id); + err = damon_select_ops(ctx, ops_id); if (err) return err; ctx->addr_unit = sys_ctx->addr_unit; /* addr_unit is respected by only DAMON_OPS_PADDR */ - if (sys_ctx->ops_id == DAMON_OPS_PADDR) + if (ops_id == DAMON_OPS_PADDR) ctx->min_region_sz = max( DAMON_MIN_REGION_SZ / sys_ctx->addr_unit, 1); ctx->pause = sys_ctx->pause; -- 2.47.3