From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792598128; b=h3l+KECiz4QSY7yH0fczhpv6mWcN9/sXvrsCwhdb3d2hKVoH6MVILYR8C12Y1NzkzfM1 T72HOst4sL+JodxHmy0JeWZonaT589c3L0Mkb6t5AieGjB+ZqBNwG7b5Gx0iF0zcJuCT7 TT0uS+yKmS7LnNETccU20Hv69znS2dgGss5+tLfb8u0/1aUJVrMlLzy2nIqXunSPSejho t13Tzx8qC1LqK/pMa+uIlIOfi8onuoq/sgq60tDToE/TGyUb2OxlKKWpmErgqjh0AZLT+ 2pST0T6fm9b176ctH+cussXC1TUYlqTg+4Yg9Ui/cEJWIoehuAYxQ09DWdPCPKCxamg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792598128; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=qYdobLlU0xLjOJP8riaKxvKAoSDn4rMN2Tuz6kPV4Zs=; b=TuxPyXkXXLlB02UEUFmzD72lByKI0tXAqjiJqrgY12r6rXuQCBWyyCuY4yPWy/XgDlTc DNvN9fbuuEY8bdIbQlwA0iZ/zgX2vomZUDwXPIKGhd09FLi/NCJX6E7lRdd2On0hHeFXs M/9+xgjaZcxL79U3nnL9Ku0BReyZ4HP/NEQ1ygPDHpQhsF/7ukd1necQ1bfAwlfKwCCvP xKwNDDH1P8QLxVqUjPo5oFcR8jpPyYZ5UElexZl3xomssjXv6tRXd5nJxYhrk28jxyhcW 1SBhDlASAYTznH3Z00S1Pu6lo2CJO57x3vSNgyuIpFs0stdzoSVHZdVvENVIl1nSmqg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=bmcyRQQo; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 37A1A606A324 for ; Wed, 21 Oct 2026 15:55:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=bmcyRQQo Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37A431F000C1; Wed, 21 Oct 2026 15:55:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792598127; bh=qYdobLlU0xLjOJP8riaKxvKAoSDn4rMN2Tuz6kPV4Zs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bmcyRQQoR0K8bnEEPSve2d61XXD8QxplOyn4is6l9SQ/rWh+WDTKM763Leky4TDUm zWDK+qe2LAK0zt6REg9fozFVSlgx0fZA0gr4GwhaFV1QkiHnqYZl7TMpwtNbziP3xW F01fypFFI7JwTGm4MUDVM5K5DT2t+rlqqLSbG2f/Nxf9pwRSuL7tiYn3CTmlvg8W1g 3EPGM4e3pAdDJ1qUKtkuvUs06Mv4iy1M9K27I3MNsB8EY3Dih9UrCU27WkWzcNpK7F /NMB2LtmSS2Faeb/ciQOUO/uE6MJjCPdRk+irerQR/1wlo/dmwiR9VCM8V6hpKRHId v127ThLuu74Fw== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Sasha Levin Subject: [PATCH 6.12.y] ext4: free the sbi after a grace period Date: Wed, 21 Oct 2026 11:55:26 -0400 Message-ID: <20261021155506.366052-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026102103-nimble-translate-97e5@gregkh> References: <2026102103-nimble-translate-97e5@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit c17b44266a1f9fcb49b894d4611d1254bf1aa313 ] ext4_get_link() follows a symlink that keeps its target in a data block in rcu pathwalk mode with ext4_getblk(EXT4_GET_BLOCKS_CACHED_NOWAIT). That reads s_mount_state in the ASSERT() of ext4_getblk() and again in ext4_es_lookup_extent(), and the lookup bumps the extent status hit or miss counter, all through sb->s_fs_info. ext4_put_super() destroys those counters, clears sb->s_fs_info and frees the sbi without waiting for a grace period. A pathwalk that is still in ext4_get_link() when the last reference to the mount goes away then dereferences a NULL s_fs_info, the freed sbi or the destroyed percpu counters. With a pathwalk held up in ext4_get_link() while the last reference goes away: KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af] RIP: 0010:ext4_getblk+0xf0/0x640 Call Trace: ext4_get_link+0x26c/0x410 pick_link+0xf96/0x1780 step_into_slowpath+0x9b8/0x1250 path_lookupat+0x484/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 vfs_fstatat+0x4d/0x90 __do_sys_newfstatat+0xa0/0x100 do_syscall_64+0x10e/0x5e0 entry_SYSCALL_64_after_hwframe+0x77/0x7f So far that has been hard to hit. umount(2) waits for a grace period in namespace_unlock() before it drops the mount, so only a mount whose last reference goes away elsewhere, like the close of a file or a chdir out of a lazily unmounted directory, can race a walker. Keep sb->s_fs_info and free the sbi together with the extent status counters after a grace period. Split the counters out of ext4_es_unregister_shrinker() for that. The shrinker still gets wasted in ext4_put_super(), the counters go with the sbi. Fixes: 6493792d3299 ("ext4: convert symlink external data block mapping to bdev") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20261009-work-fixes-rcu-v1-1-7446d2d335e6@kernel.org Signed-off-by: Christian Brauner (Amutable) [ sashal: omitted ext4_es_destroy_stats() integration with the extent KUnit tests ] Signed-off-by: Sasha Levin --- fs/ext4/ext4.h | 2 ++ fs/ext4/extents_status.c | 7 ++++++- fs/ext4/extents_status.h | 1 + fs/ext4/super.c | 13 +++++++++++-- 4 files changed, 20 insertions(+), 3 deletions(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 21de942bb6fb3..3e0c29434ae38 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1663,6 +1663,8 @@ struct ext4_sb_info { struct list_head s_es_list; /* List of inodes with reclaimable extents */ long s_es_nr_inode; struct ext4_es_stats s_es_stats; + /* ext4_get_link() reads the sbi in rcu pathwalk */ + struct rcu_head s_rcu; struct mb_cache *s_ea_block_cache; struct mb_cache *s_ea_inode_cache; spinlock_t s_es_lock ____cacheline_aligned_in_smp; diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c index c786691dabd3d..425a613683c0a 100644 --- a/fs/ext4/extents_status.c +++ b/fs/ext4/extents_status.c @@ -1766,12 +1766,17 @@ int ext4_es_register_shrinker(struct ext4_sb_info *sbi) } void ext4_es_unregister_shrinker(struct ext4_sb_info *sbi) +{ + shrinker_free(sbi->s_es_shrinker); +} + +/* ext4_get_link() bumps the hit and miss counters in rcu pathwalk */ +void ext4_es_destroy_stats(struct ext4_sb_info *sbi) { percpu_counter_destroy(&sbi->s_es_stats.es_stats_cache_hits); percpu_counter_destroy(&sbi->s_es_stats.es_stats_cache_misses); percpu_counter_destroy(&sbi->s_es_stats.es_stats_all_cnt); percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt); - shrinker_free(sbi->s_es_shrinker); } /* diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h index 4424232de2989..c1e45f6ab6647 100644 --- a/fs/ext4/extents_status.h +++ b/fs/ext4/extents_status.h @@ -237,6 +237,7 @@ static inline void ext4_es_store_pblock_status(struct extent_status *es, extern int ext4_es_register_shrinker(struct ext4_sb_info *sbi); extern void ext4_es_unregister_shrinker(struct ext4_sb_info *sbi); +extern void ext4_es_destroy_stats(struct ext4_sb_info *sbi); extern int ext4_seq_es_shrinker_info_show(struct seq_file *seq, void *v); diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 08f84ed65ad1c..25aae8165f070 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1289,6 +1289,14 @@ static void ext4_flex_groups_free(struct ext4_sb_info *sbi) } } +static void ext4_put_sbi_rcu(struct rcu_head *head) +{ + struct ext4_sb_info *sbi = container_of(head, struct ext4_sb_info, s_rcu); + + ext4_es_destroy_stats(sbi); + kfree(sbi); +} + static void ext4_put_super(struct super_block *sb) { struct ext4_sb_info *sbi = EXT4_SB(sb); @@ -1381,7 +1389,6 @@ static void ext4_put_super(struct super_block *sb) ext4_stop_mmpd(sbi); brelse(sbi->s_sbh); - sb->s_fs_info = NULL; /* * Now that we are completely done shutting down the * superblock, we need to actually destroy the kobject. @@ -1396,7 +1403,8 @@ static void ext4_put_super(struct super_block *sb) #if IS_ENABLED(CONFIG_UNICODE) utf8_unload(sb->s_encoding); #endif - kfree(sbi); + /* ext4_get_link() reads the sbi and the counters in rcu pathwalk */ + call_rcu(&sbi->s_rcu, ext4_put_sbi_rcu); } static struct kmem_cache *ext4_inode_cachep; @@ -5659,6 +5667,7 @@ failed_mount8: __maybe_unused } failed_mount3a: ext4_es_unregister_shrinker(sbi); + ext4_es_destroy_stats(sbi); failed_mount3: /* flush s_sb_upd_work before sbi destroy */ flush_work(&sbi->s_sb_upd_work); -- 2.53.0