From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EE9DA37CD33 for ; Tue, 29 Sep 2026 13:52:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790689955; cv=none; b=FZPYkujSlmK+wpN58WTMZNMu6gCUc4gqoLRFeRKKC2+0wRdebK6e6JFonGcQKB+QN2nMsxdz1NrHvQQpmEVm5x4Gl32irFI/bGp74dHM1wxhNYaBE0x+9+k/VVxPCGT3nWZaehThesSsfVQt/bcFmnAjt8VXAYKMuB52zCFb8LE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790689955; c=relaxed/simple; bh=XRCPqYUjJXRf6MLfVDLPZAJ+WEAtcCGP8dnA0jy6Mxw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GMBHHhAIpKo4tAEa5vl4OmsqOCTqg/SNolWapJkmFzop6Ce6NnAoSBOuzro3TCqKr3SdikbbsqurIUf2dPwPs8/GfNqkejBZlUioeLYxwgBAO37aG/5hk+RWnhLAtlCf3u5g7QZZZvX2UIkSAtRrwt8euHejvGqCar/J5ldZXk4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Nk1dDbKV; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Nk1dDbKV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 366601F0089A; Tue, 29 Sep 2026 13:52:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790689953; bh=Gwb5It4Uy9w8eNIyqNdPNWlorYJMEBGp4fzEN0sHaDE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Nk1dDbKV4O7DutV0P0SGtss0BWjrEMURJD8rMXVHpalC6dTDSBpdN/kS4Hb2t9vdm AncpixqRWhXSeyFhsxQ41HQwW7N2Qfynk173hm5CtEXi9SmTffuonnWL2dVtfXC3Po hEAkUNWu8n4VO2kmtq6btbFC5EK8xdkXwj0iDbzy/EHY51QzZMEdBN35pNLeATFLVy 6uGGci9fEk803ExaaiUFNneC1zxD6ftCIAuBXf/8iEd9tQkJ/puVKmre7Us6ZBLgHX fqTK2ZAmpG6kAy2QAQq4pKiDOjb1D31AiLnrh4VU/4t/NyE1vUnK9Yopyz6HWxEcUo R7Gd5+p0EsLww== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Karl Mehltretter , Jan Kara , Sasha Levin Subject: [PATCH 7.2.y 3/3] super: make iterate_supers_type() deletion-safe Date: Tue, 29 Sep 2026 09:52:30 -0400 Message-ID: <20260929135230.3522081-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260929135230.3522081-1-sashal@kernel.org> References: <2026092911-clunky-same-c5c5@gregkh> <20260929135230.3522081-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit 2d2a2d7aa98741b58f54cacc99b52024e4d865f9 ] iterate_supers_type() drops sb_lock while invoking the callback and keeps only a passive reference to the current superblock. That reference keeps the object allocated, but does not keep its s_instances node linked. After the iterator releases s_umount, final teardown can unlink the current s_instances node. The iterator then advances through a reinitialized node. With the current hlist it stops without visiting the remaining superblocks. The unlink moved from generic_shutdown_super() to kill_super_notify(), but the cursor lifetime has been unsafe since the helper was introduced. The CIFS DFS lookup can consequently miss a matching superblock and return -EINVAL. Move removal from fs_supers to put_super(), alongside removal from super_blocks, so a passive reference keeps both list nodes linked. Keep the filesystem module reference until then, since unlinking s_instances may touch type->fs_supers. Make sget_fc() skip SB_DEAD superblocks before invoking test(), and set SB_DEAD under sb_lock to serialize with those callbacks. This allows kernfs to free its private information after kill_anon_super() returns. Keep matching SB_DYING superblocks until SB_DEAD is set so concurrent mounts still wait for teardown before retrying. Fixes: 43e15cdbefea ("new helper: iterate_supers_type()") Reported-by: Karl Mehltretter Closes: https://lore.kernel.org/r/20260903013336.92081-1-kmehltretter@gmail.com Suggested-by: Jan Kara Cc: stable@vger.kernel.org Tested-by: Karl Mehltretter [kmehltretter: supplied the commit message] Signed-off-by: Karl Mehltretter Link: https://patch.msgid.link/20260909193034.7467-1-kmehltretter@gmail.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner (Amutable) [ adjusted kill_super_notify() context for missing device-to-superblock table cleanup. ] Signed-off-by: Sasha Levin --- fs/kernfs/mount.c | 4 ++-- fs/super.c | 39 +++++++++++++++++++-------------------- 2 files changed, 21 insertions(+), 22 deletions(-) diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c index f183a96778b9a..a57399021c8b0 100644 --- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -434,8 +434,8 @@ void kernfs_kill_sb(struct super_block *sb) up_write(&root->kernfs_supers_rwsem); /* - * Remove the superblock from fs_supers/s_instances - * so we can't find it, before freeing kernfs_super_info. + * Mark the superblock dead so sget_fc() can't find it, + * before freeing kernfs_super_info. */ kill_anon_super(sb); kfree(info); diff --git a/fs/super.c b/fs/super.c index 2399bb3a17527..addf3ad54a583 100644 --- a/fs/super.c +++ b/fs/super.c @@ -410,15 +410,19 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags, void put_super(struct super_block *s) { if (refcount_dec_and_test(&s->s_passive)) { + struct file_system_type *type = s->s_type; spin_lock(&sb_lock); list_del_init(&s->s_list); + hlist_del_init(&s->s_instances); spin_unlock(&sb_lock); WARN_ON(s->s_dentry_lru.node); WARN_ON(s->s_inode_lru.node); WARN_ON(s->s_mounts); call_rcu(&s->rcu, destroy_super_rcu); + /* The unlink above may touch type->fs_supers, so drop it last. */ + put_filesystem(type); } } @@ -430,24 +434,17 @@ static void kill_super_notify(struct super_block *sb) if (sb->s_flags & SB_DEAD) return; - /* - * Remove it from @fs_supers so it isn't found by new - * sget_fc() walkers anymore. Any concurrent mounter still - * managing to grab a temporary reference is guaranteed to - * already see SB_DYING and will wait until we notify them about - * SB_DEAD. - */ - spin_lock(&sb_lock); - hlist_del_init(&sb->s_instances); - spin_unlock(&sb_lock); - /* * Let concurrent mounts know that this thing is really dead. - * We don't need @sb->s_umount here as every concurrent caller - * will see SB_DYING and either discard the superblock or wait - * for SB_DEAD. + * sget_fc() skips SB_DEAD superblocks and calls test() under + * sb_lock, so set it under sb_lock: once we return no test() + * runs on this superblock anymore and none will start. Everyone + * else already saw SB_DYING and either discarded the superblock + * or waits for SB_DEAD. */ + spin_lock(&sb_lock); super_wake(sb, SB_DEAD); + spin_unlock(&sb_lock); } /** @@ -474,7 +471,6 @@ void deactivate_locked_super(struct super_block *s) list_lru_destroy(&s->s_dentry_lru); list_lru_destroy(&s->s_inode_lru); - put_filesystem(fs); put_super(s); } else { super_unlock_excl(s); @@ -661,12 +657,12 @@ void generic_shutdown_super(struct super_block *sb) } /* * Broadcast to everyone that grabbed a temporary reference to this - * superblock before we removed it from @fs_supers that the superblock - * is dying. Every walker of @fs_supers outside of sget_fc() will now - * discard this superblock and treat it as dead. + * superblock that it is dying. Every walker of @fs_supers outside + * of sget_fc() will now discard this superblock and treat it as + * dead. * - * We leave the superblock on @fs_supers so it can be found by - * sget_fc() until we passed sb->kill_sb(). + * sget_fc() keeps finding the superblock until SB_DEAD is set, so + * a concurrent mounter waits until we passed sb->kill_sb(). */ super_wake(sb, SB_DYING); super_unlock_excl(sb); @@ -745,6 +741,9 @@ struct super_block *sget_fc(struct fs_context *fc, spin_lock(&sb_lock); if (test) { hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) { + /* Only unlinked at the last passive reference. */ + if (super_flags(old, SB_DEAD)) + continue; if (test(old, fc)) goto share_extant_sb; } -- 2.53.0