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Tue, 27 Oct 2026 13:31:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=narfation.org; s=20121; t=1793107888; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=CtmBFZqy7yb/5wYHUpcMRHp04sS85G1RGMRlAVhNk2A=; b=cXezh2H/E7GewGqyaKqbpKa1w11CeXbx9IMUt3T/mRS60BwkE7jF4zMa2QIXe5S02UgcA7 bqPEq2xhWCnJRcSD1RsrGGVzcezhxXyrKOhs2PXsElBtybJx0aU+sKTsnJyO1IfIFuBSZy oA4wBBQ08Jt0Fj+K+8GMH+TBx3BnaTk= From: Sven Eckelmann To: sw@simonwunderlich.de, netdev-bot+sashiko@kernel.org Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, b.a.t.m.a.n@lists.open-mesh.org, sashiko-bot@kernel.org Subject: Re: [PATCH net 09/10] batman-adv: tt: don't drop local events queued during TVLV update Date: Tue, 27 Oct 2026 14:31:25 +0100 Message-ID: <3709090.V25eIC5XRa@ripper> In-Reply-To: <179309132364.3134.18203109296409373363@kernel.org> References: <20261026085309.1074911-10-sw@simonwunderlich.de> <179309132364.3134.18203109296409373363@kernel.org> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart3771355.LM0AJKV5NW"; micalg="pgp-sha512"; protocol="application/pgp-signature" --nextPart3771355.LM0AJKV5NW Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8"; protected-headers="v1" From: Sven Eckelmann To: sw@simonwunderlich.de, netdev-bot+sashiko@kernel.org Date: Tue, 27 Oct 2026 14:31:25 +0100 Message-ID: <3709090.V25eIC5XRa@ripper> In-Reply-To: <179309132364.3134.18203109296409373363@kernel.org> MIME-Version: 1.0 On Tuesday, 27 October 2026 09:55:23 CET netdev-bot+sashiko@kernel.org wrote: [...] > > diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c > > index 24054077cf3db..6774484f1c573 100644 > > --- a/net/batman-adv/translation-table.c > > +++ b/net/batman-adv/translation-table.c > > @@ -1327,11 +1327,18 @@ static void batadv_tt_tvlv_container_update(struct batadv_priv *bat_priv) > > int tt_diff_entries_num = 0; > > bool drop_changes = false; > > size_t tt_extra_len = 0; > > + LIST_HEAD(changes_list); > > int tt_change_len = 0; > > int tt_diff_len; > > u16 tvlv_len; > > > > + /* atomically get the list of changes */ > > + spin_lock_bh(&bat_priv->tt.changes_list_lock); > > + list_splice_init(&bat_priv->tt.changes_list, &changes_list); > > tt_diff_entries_num = READ_ONCE(bat_priv->tt.local_changes); > > + WRITE_ONCE(bat_priv->tt.local_changes, 0); > > + spin_unlock_bh(&bat_priv->tt.changes_list_lock); > > [Severity: Medium] > This isn't a bug introduced by this patch, but the window left open at the > end of the commit message seems to have a worse effect than described. An > event in that window can be lost, not just announced under the wrong TTVN > or CRC. > > batadv_tt_local_commit_changes_nolock() makes its decisions from a lockless > read, before this splice happens: [...] > Would either of these close the window: taking the snapshot in > batadv_tt_local_commit_changes_nolock() before the local_changes check and > passing the list down, or not consuming the list in the non-committing > branch? Out-of-scope for this patch and handled in another pending patch https://patchwork.open-mesh.org/project/b.a.t.m.a.n./patch/20261025-tt-tvlv-changes-check-v1-1-c12b246c0956@narfation.org/ > [ ... ] > > > @@ -1349,19 +1356,23 @@ static void batadv_tt_tvlv_container_update(struct batadv_priv *bat_priv) > > > > tvlv_len = batadv_tt_prepare_tvlv_local_data(bat_priv, &tt_data, > > &tt_change, &tt_diff_len); > > - if (!tvlv_len) > > + if (!tvlv_len) { > > + /* the TTVN of the changes is lost and the other nodes will > > + * have to request the full table anyway > > + */ > > + list_for_each_entry_safe(entry, safe, &changes_list, list) { > > + list_del(&entry->list); > > + kmem_cache_free(batadv_tt_change_cache, entry); > > + } > > return; > > + } > > [Severity: Low] > Does this statement in the commit message hold when the node is idle? > > "The changes can no longer be kept for the next round when the TVLV > buffer allocation fails. But they would be sent with a skipped TTVN > anyway, so the other nodes have to request the full table in this case > either way." > > When batadv_tt_prepare_tvlv_local_data() fails here, the caller > batadv_tt_local_commit_changes_nolock() has already bumped tt.vn to N, > updated the CRCs and reset ogm_append_cnt to BATADV_TT_OGM_APPEND_MAX. No > new container is registered, so OGMs keep carrying the old container (ttvn > N-1 with the old CRCs). [...] > Before this patch, the !tvlv_len return left the list and counter in place. > The next interval then bumped the TTVN to N+1, and peers saw the skipped > TTVN immediately. Why would the first round fail and the second round not? Please don't start with kmalloc-failures - this would open a completely different can of worms related to containers and OGMs. > With this change, can peers learn about the committed local changes several > OGM intervals later, with no TTVN skipped at all? Re-queueing the changes > isn't simple because __batadv_tt_local_event() expects at most one queued > change per (addr, vid). Would it be enough to force a TTVN bump or commit in > the next round instead? What is proposed here? if (!tvlv_len) { /* the changes are lost and the other nodes have to request the * full table. Announce the new TTVN in the next OGM interval * and don't answer TT requests for it with the stale changeset * of the previous TTVN */ list_for_each_entry_safe(entry, safe, &changes_list, list) { list_del(&entry->list); kmem_cache_free(batadv_tt_change_cache, entry); } spin_lock_bh(&bat_priv->tt.last_changeset_lock); kfree(bat_priv->tt.last_changeset); bat_priv->tt.last_changeset = NULL; bat_priv->tt.last_changeset_len = 0; spin_unlock_bh(&bat_priv->tt.last_changeset_lock); /* announce the already committed TTVN in the next OGM interval * instead of waiting for BATADV_TT_OGM_APPEND_MAX idle rounds */ atomic_set(&bat_priv->tt.ogm_append_cnt, 0); return; } https://www.open-mesh.org/issues/485 https://patchwork.open-mesh.org/project/b.a.t.m.a.n./patch/20261027-tt-tvlv-alloc-fail-v1-1-02058bcc4595@narfation.org/ > > [Severity: Medium] > Can this error path leave a stale bat_priv->tt.last_changeset that is later > served under the new TTVN? Which it did even before the patch [...] > The new comment says "the other nodes will have to request the full table > anyway", but here the first request is a diff request. Which makes the statements untrue because of "first request"? Which is not even mentioned in the comment. > Should this path > free last_changeset and set it to NULL under last_changeset_lock, or force > the next round to bump the TTVN? https://www.open-mesh.org/issues/485 Regards, Sven --nextPart3771355.LM0AJKV5NW Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part. Content-Transfer-Encoding: 7Bit -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQS81G/PswftH/OW8cVND3cr0xT1ywUCauCnrQAKCRBND3cr0xT1 y950AQDuGG0HAjKHF4ix691UqCNIHbtVk+Us9my7NayEmeo/2QD+NrUQvy8K/xI8 lvqkE8wvR7H+r9c4YCn9u+oNkcR8cwQ= =Se1b -----END PGP SIGNATURE----- --nextPart3771355.LM0AJKV5NW--