From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4FCC53AA4E1; Mon, 20 Apr 2026 18:10:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776708636; cv=none; b=LFAN4Scge5dSwwIrriHk3qrWUdD27Xbel3Tpkk4OfJLv7IxANyB3rpzOQ6p/7fWHUpj+2LNuJ509ntJODUHGJyiMUFyTvMUWI+oulzZFuOCCuVG+J5oqAp422Dx1bgPU6nlpdCAQhiAZCRdn/ys1xLFGAd1wOrCbEyw5w6AlhAA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776708636; c=relaxed/simple; bh=pWrR8Z0Td/iCp1eVgaoH6EZ4EwyB4hXurSX8ZNwlu2c=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=E971+r8BqsuxxASiRmAymLct1g9UnRMW1nVI7WDsiFm8/UBzd/UrXNuCANJYNFGTEdQ1vEhgNIi8xAPgRcN3FE+9MfGekqpt71NcMBP9kgL48CQErzBvvDIBx4sTr0Xi89IfCT6CRr6MhuacawI46XT4YsqaR3z3tDDJz3hpKhI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mKR3+zMo; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mKR3+zMo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 356C2C2BCB8; Mon, 20 Apr 2026 18:10:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776708636; bh=pWrR8Z0Td/iCp1eVgaoH6EZ4EwyB4hXurSX8ZNwlu2c=; h=Date:From:To:Cc:Subject:References:From; b=mKR3+zMo4XMXE0JIX6OuK5UCPM1ZXgZJ58APv8pjIiT3Rxmj3qBRGCX4Pd8GAE3/Y Euhz2XbGFS/Y3EIzOm5W2wvQYgwEnpPGNP1mTIm0KX+1Tk85ViruPFQ6hf/qEMQxBC o18vTFLYkeybCpgL7OCHOHHSq+LwuTGxykmsZ4ea/UrnWXCHSXVoXonbaslaMqgqPT ByWJURApCHnfAKofXNh+R6yaOCYuRKa9+e1O6SN7xpEzh0Ywpptgo7i8AZOYL5gqWA f3Y9gZyRMkALVOtKAerGq4HOtPkBvx+zlXCNQX6P746rdzvFVYQd4vtBNpOcFA2/6G P3Fxx6evW4wfg== Received: from rostedt by gandalf with local (Exim 4.99.1) (envelope-from ) id 1wEt6a-00000006nIo-27Wy; Mon, 20 Apr 2026 14:12:20 -0400 Message-ID: <20260420181220.362882530@kernel.org> User-Agent: quilt/0.69 Date: Mon, 20 Apr 2026 14:11:53 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org, David Carlier Subject: [for-linus][PATCH 2/2] eventfs: Hold eventfs_mutex and SRCU when remount walks events References: <20260420181151.771404678@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: David Carlier Commit 340f0c7067a9 ("eventfs: Update all the eventfs_inodes from the events descriptor") had eventfs_set_attrs() recurse through ei->children on remount. The walk only holds the rcu_read_lock() taken by tracefs_apply_options() over tracefs_inodes, which is wrong: - list_for_each_entry over ei->children races with the list_del_rcu() in eventfs_remove_rec() -- LIST_POISON1 deref, same shape as d2603279c7d6. - eventfs_inodes are freed via call_srcu(&eventfs_srcu, ...). rcu_read_lock() does not extend an SRCU grace period, so ti->private can be reclaimed under the walk. - The writes to ei->attr race with eventfs_set_attr(), which holds eventfs_mutex. Reproducer: while :; do mount -o remount,uid=$((RANDOM%1000)) /sys/kernel/tracing; done & while :; do echo "p:kp submit_bio" > /sys/kernel/tracing/kprobe_events echo > /sys/kernel/tracing/kprobe_events done Wrap the events portion of tracefs_apply_options() in eventfs_remount_lock()/_unlock() that take eventfs_mutex and srcu_read_lock(&eventfs_srcu). eventfs_set_attrs() doesn't sleep so the nested rcu_read_lock() is fine; lockdep_assert_held() pins the contract. Comment in tracefs_drop_inode() said "RCU cycle" -- it is SRCU. Fixes: 340f0c7067a9 ("eventfs: Update all the eventfs_inodes from the events descriptor") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260418191737.10289-1-devnexen@gmail.com Signed-off-by: David Carlier Signed-off-by: Steven Rostedt --- fs/tracefs/event_inode.c | 14 ++++++++++++++ fs/tracefs/inode.c | 5 ++++- fs/tracefs/internal.h | 3 +++ 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 8dd554508828..26b6453de30e 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -244,6 +244,8 @@ static void eventfs_set_attrs(struct eventfs_inode *ei, bool update_uid, kuid_t { struct eventfs_inode *ei_child; + lockdep_assert_held(&eventfs_mutex); + /* Update events// */ if (WARN_ON_ONCE(level > 3)) return; @@ -886,3 +888,15 @@ void eventfs_remove_events_dir(struct eventfs_inode *ei) d_invalidate(dentry); d_make_discardable(dentry); } + +int eventfs_remount_lock(void) +{ + mutex_lock(&eventfs_mutex); + return srcu_read_lock(&eventfs_srcu); +} + +void eventfs_remount_unlock(int srcu_idx) +{ + srcu_read_unlock(&eventfs_srcu, srcu_idx); + mutex_unlock(&eventfs_mutex); +} diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 5602baf980f6..1e8a78c5e996 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -313,6 +313,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount) struct inode *inode = d_inode(sb->s_root); struct tracefs_inode *ti; bool update_uid, update_gid; + int srcu_idx; umode_t tmp_mode; /* @@ -337,6 +338,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount) update_uid = fsi->opts & BIT(Opt_uid); update_gid = fsi->opts & BIT(Opt_gid); + srcu_idx = eventfs_remount_lock(); rcu_read_lock(); list_for_each_entry_rcu(ti, &tracefs_inodes, list) { if (update_uid) { @@ -358,6 +360,7 @@ static int tracefs_apply_options(struct super_block *sb, bool remount) eventfs_remount(ti, update_uid, update_gid); } rcu_read_unlock(); + eventfs_remount_unlock(srcu_idx); } return 0; @@ -403,7 +406,7 @@ static int tracefs_drop_inode(struct inode *inode) * This inode is being freed and cannot be used for * eventfs. Clear the flag so that it doesn't call into * eventfs during the remount flag updates. The eventfs_inode - * gets freed after an RCU cycle, so the content will still + * gets freed after an SRCU cycle, so the content will still * be safe if the iteration is going on now. */ ti->flags &= ~TRACEFS_EVENT_INODE; diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index d83c2a25f288..a4a7f8431aff 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h @@ -76,4 +76,7 @@ struct inode *tracefs_get_inode(struct super_block *sb); void eventfs_remount(struct tracefs_inode *ti, bool update_uid, bool update_gid); void eventfs_d_release(struct dentry *dentry); +int eventfs_remount_lock(void); +void eventfs_remount_unlock(int srcu_idx); + #endif /* _TRACEFS_INTERNAL_H */ -- 2.51.0