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Fri, 20 Mar 2026 17:34:59 +0100 (CET) From: Josh Law To: SeongJae Park , Andrew Morton Cc: damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Law , stable@vger.kernel.org Subject: [PATCH v2] mm/damon/sysfs: check contexts->nr in repeat_call_fn Date: Fri, 20 Mar 2026 16:34:56 +0000 Message-Id: <20260320163456.177750-3-objecting@objecting.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260320163456.177750-1-objecting@objecting.org> References: <20260320163456.177750-1-objecting@objecting.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2A12BC000B X-Stat-Signature: oxxyusg449fctr95c4a85dnp1duogz3i X-Rspam-User: X-HE-Tag: 1774024512-499662 X-HE-Meta: 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 epXfjYNe zAZaKaAyH7auFE8BSBQstSpP67Xe5OzxLAgGqzRTVtDPcmYCwTaSWyRQmmq4615RhC3YKBPe3V1nW2lYfsQSlCetouG+fSly/KnqWsi8nqnaeOUU4GSptm8GnpnJRDRS6COK4ffQ5J7crEPJb+k9k9JaVQyxfok9a4uBYZNhUucIQzraQJbvhQzqmPHvBiso6rV7olCbqfhq2dkazkPHDh9OQE1IP92BqzJhri8tRaJuI2f9O8vX5gkpjKZ/r1nDZ00TlpHEKREcpdVCgwsibKz7g+IWkqb9hSUW91c9SdozrZ0Ol5XrxN2vf36x5C6WP4Kr3m7NfsqduT+ClpxdbMIhNB5liADfFI3pCfnjgnfrV10tf11VnepnJlsE9cYAOHat9ZLcPgCP0PcUMTaGL2Iv8OkPuqqrGYesQWVZmWpshnOo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_sysfs_repeat_call_fn() calls damon_sysfs_upd_tuned_intervals(), damon_sysfs_upd_schemes_stats(), and damon_sysfs_upd_schemes_effective_quotas() without checking contexts->nr. If nr_contexts is set to 0 via sysfs while DAMON is running, these functions dereference contexts_arr[0] and cause a NULL pointer dereference. Add the missing check. Fixes: d809a7c64ba8 ("mm/damon/sysfs: implement refresh_ms file internal work") Cc: # 6.17.x Signed-off-by: Josh Law Reviewed-by: SeongJae Park --- mm/damon/sysfs.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index ddc30586c0e6..6a44a2f3d8fc 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1620,9 +1620,12 @@ static int damon_sysfs_repeat_call_fn(void *data) if (!mutex_trylock(&damon_sysfs_lock)) return 0; + if (sysfs_kdamond->contexts->nr != 1) + goto out; damon_sysfs_upd_tuned_intervals(sysfs_kdamond); damon_sysfs_upd_schemes_stats(sysfs_kdamond); damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond); +out: mutex_unlock(&damon_sysfs_lock); return 0; } -- 2.34.1