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=1792594168; b=37xhUbPhZE6RwHAWSIFiDcvFG8XRhiqcm5UNyPZls0XjdSMqEu1D5DRko574EcmySTtD MWSEa1xrRxLP+/P5IRAZvpSoY6T6Q7C/wRfvDXHPSkvDNsU10cwN8ssf2DU8udpWDGVqN KBBS58zQUJaKD2iPFlJXjsDzLUkUdH5JGqOVPaSPIqkXAkVQUkL4hj918WHe1d53ERmIg TG6B3qH3lCebs7e5jHJNUOJbgxwT+ZTqMZL24oLKHNYAwC3iTC1BgspYsTYs0DQ3FegrU o+YogwpFMY/H7xV4skPFnhoT2TvT/CfFcyP07R4Rairyj/jtW5myjxHIwLmRkaV2yyQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792594168; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=ePKyqodRCelJe/wB57fTOHJ+51NlW8lNp7JPgnOG4lI=; b=NYOJG0L+Y0UkBPJn9V+rw+l77j+R5Zkz9tXQoBYK5OeB0ZW2D6JMaTymGNYZzzi/1Q+s IcG+SDj9AnE5ZoSm9dQjcOUa+W/O8WEIz3/yPe+J5DNiWydsXX03B0dlkWm26C3E3zvcU p+U/Ivv4fIxpmqtfLpupa06SXk/kXIMqaU+eUpt8gM82SwY2XsP+2RLcg3tvDFvPqqAM5 vBMDID9YaZkLqb9erLCTD6Vg75W5WKaf+FcwKB1E98290U3anvrsG9m6nb4R9gv/NKW5A UARacsKMF+rfDp3DNYQG8nRs9phUlf8/ylqZsfrKJ2gg4JmmxgfKRudHPaoYI17Ty7w== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=ZYHAEVCu; 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 C71A3606A31D for ; Wed, 21 Oct 2026 14:49:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=ZYHAEVCu Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC3B11F000C2; Wed, 21 Oct 2026 14:49:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792594167; bh=ePKyqodRCelJe/wB57fTOHJ+51NlW8lNp7JPgnOG4lI=; h=Subject:To:Cc:From:Date; b=ZYHAEVCuk2fEXjcsFZOr0J6QVbt2QxKg9EsglxaK5ugOwm3ebPZTp7rCkmkzmlsEP YQjzp7WWCE7fKKBHUMYO2zH+p9LLPW0Sp54k9mPlxroaOj3RwdBhj5nAiZpEzKC/Uj yXNtL0uZbDvifVNh8zbvwY2oOlvvmHi1um5rTEn8= Subject: FAILED: patch "[PATCH] ext4: free the sbi after a grace period" failed to apply to 6.1-stable tree To: brauner@kernel.org Cc: From: Date: Wed, 21 Oct 2026 16:38:04 +0200 Message-ID: <2026102104-sensitive-overnight-fe0d@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-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x c17b44266a1f9fcb49b894d4611d1254bf1aa313 # git commit -s git send-email --to '' --in-reply-to '2026102104-sensitive-overnight-fe0d@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From c17b44266a1f9fcb49b894d4611d1254bf1aa313 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 9 Oct 2026 23:51:51 +0200 Subject: [PATCH] ext4: free the sbi after a grace period 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) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 724a27e8be61..af70bb26bb54 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1774,6 +1774,8 @@ 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; diff --git a/fs/ext4/extents-test.c b/fs/ext4/extents-test.c index c3836ecb89f9..2e997f228330 100644 --- a/fs/ext4/extents-test.c +++ b/fs/ext4/extents-test.c @@ -151,6 +151,7 @@ static void extents_kunit_exit(struct kunit *test) sbi = k_ctx.k_ei->vfs_inode.i_sb->s_fs_info; ext4_es_unregister_shrinker(sbi); + ext4_es_destroy_stats(sbi); deactivate_super(sbi->s_sb); kfree(sbi); kfree(k_ctx.k_ei); @@ -340,6 +341,7 @@ static int extents_kunit_init(struct kunit *test) k_ctx.k_data = NULL; ext4_es_unregister_shrinker(sbi); + ext4_es_destroy_stats(sbi); out_deactivate: deactivate_locked_super(sb); kfree(sbi); diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 76038b6c3655..3bf0a6cdbec2 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -6409,6 +6409,7 @@ EXPORT_SYMBOL_FOR_EXT4_TEST(__ext4_ext_dirty); EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_ext_zeroout); EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_es_register_shrinker); EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_es_unregister_shrinker); +EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_es_destroy_stats); EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_map_create_blocks); EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_es_init_tree); EXPORT_SYMBOL_FOR_EXT4_TEST(ext4_es_lookup_extent); diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c index 6e4a191e8219..018b6146b9d8 100644 --- a/fs/ext4/extents_status.c +++ b/fs/ext4/extents_status.c @@ -1881,12 +1881,17 @@ 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 f3396cf32b44..01cddcaaa68e 100644 --- a/fs/ext4/extents_status.h +++ b/fs/ext4/extents_status.h @@ -238,6 +238,7 @@ 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 d636b89090a2..3ace06b4f9e3 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1279,6 +1279,14 @@ 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); @@ -1374,7 +1382,6 @@ 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. @@ -1387,7 +1394,8 @@ 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; @@ -5806,6 +5814,7 @@ failed_mount8: __maybe_unused /* Drain deferred EA inode iputs from journal replay */ flush_delayed_work(&sbi->s_ea_inode_work); 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);