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[98.51.119.100]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2d561bde70csm21099493eec.15.2026.04.13.14.27.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Apr 2026 14:27:27 -0700 (PDT) From: Milos Nikic To: jack@suse.cz, tytso@mit.edu, linux-ext4@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Milos Nikic Subject: [PATCH] jbd2: enforce power-of-two default revoke hash size at compile time Date: Mon, 13 Apr 2026 14:27:24 -0700 Message-ID: <20260413212724.127035-1-nikic.milos@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The jbd2 revoke table relies on bitwise AND operations for fast hash indexing, which requires the hash table size to be a strict power of two. Currently, this requirement is only enforced at runtime via a J_ASSERT in jbd2_journal_init_revoke(). While this successfully catches invalid dynamic allocations, it means a developer accidentally modifying the hardcoded JOURNAL_REVOKE_DEFAULT_HASH macro will experience a system panic upon mounting the filesystem during testing. Add a BUILD_BUG_ON() in journal_init_common() to validate the default macro at compile time. This acts as an immediate, zero-overhead safeguard, preventing compilation entirely if the default hash size is mathematically invalid. Signed-off-by: Milos Nikic --- fs/jbd2/journal.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 4f397fcdb13c..62b36a2fc4e2 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -1565,6 +1565,7 @@ static journal_t *journal_init_common(struct block_device *bdev, /* The journal is marked for error until we succeed with recovery! */ journal->j_flags = JBD2_ABORT; + BUILD_BUG_ON(!is_power_of_2(JOURNAL_REVOKE_DEFAULT_HASH)); /* Set up a default-sized revoke table for the new mount. */ err = jbd2_journal_init_revoke(journal, JOURNAL_REVOKE_DEFAULT_HASH); if (err) -- 2.53.0