From nobody Thu Apr 2 22:07:14 2026 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4EF4C35E553 for ; Thu, 12 Feb 2026 21:58:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770933516; cv=none; b=oYet77keBl4lgcekvcVdYKZtHeEdJ6P6brUsa16JgvTr1AQpwVFNSroQwY9+skkAVPG6nkppgDpScXaPQbfiAtMin1NkZaE60/UuWgk5RvKgVl5+b+rydVD+d1ObrL/GqW8TUVg4frZ/rvcX34suHWmIVXSrwnDF7K/u9LzgY0Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770933516; c=relaxed/simple; bh=JZj4LpEl8D/f9PumooC8+GYc0Dg8nxxVo/kQgge2600=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=fuPfhfaIf0/7jyyNGO3ZxbxVTeQP9Xzcnh50qbv4wNRpJyqkW8+IpmE0sajvY6rbjDBPFCR5E+ipG35eXmkY3Dqx1z13D3OWCqRYuVTKIxd5FmPUlhP87aAbibNmg3B8dJy7RuHfzY9kGGjDQ/dLNEsFKq88uctBBh4VxM4Bae4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--tjmercier.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=WXnY8bkK; arc=none smtp.client-ip=209.85.214.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--tjmercier.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="WXnY8bkK" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-2aad3380076so14116855ad.1 for ; Thu, 12 Feb 2026 13:58:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1770933515; x=1771538315; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=ajT1DeXeAjXwu6HaXbFv5+sD4L7P9mYZ5NNigjqhjfQ=; b=WXnY8bkKdBf5dKEscJFH2TB+k5QETGokMg0QvFEedO2G5/puiVWwC6Hy5Ld1zCDKrw Iu+5G1LG8Pi6fVO0FRyoNwWonRTzzFsL0PLEIEC7uOZ9MJrG1L0fKgHEJ1KVkRNXDLue lrcQGHd/IsSmFSA33wiYTWFZMTh4e1FyAztXCJDVLD6mAA6IBtx6QHgK9RpTlcxdaIi1 ESCAjOp66gX2Yml+fDvOOM7JG2Y36+TSeqHxDDu6sreMYn3l2/hZyw28iv0NsF+wn5nL EX+4cTWC39dp/LCm4fEJLVUQXevKc85fErseWVGkEkYoWXSianGd5qu519EGQRvb+vDI 2P0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770933515; x=1771538315; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ajT1DeXeAjXwu6HaXbFv5+sD4L7P9mYZ5NNigjqhjfQ=; b=o66JtBna/TvmSZWE0NznfJKsClym2vBVLxu+QYuvpqgdvrn2e9GIkvCetKmjH/WZB0 P7UOntRMu3Vf5tbcTPaNnIuVLswYznJqeipLur0Q2SGUJEyYyi6BA/kEQPWLiHw7Fb2b K9yRGmv3J0Vj7wqlNWVOSZ4S5/A+HJ2rK4tH1zcDUo29NUzEoC21NbWQ5C2zsO24ViL0 fUjjTUtabRwgONA21yp8dwKF39L7GN7JPyNmEpP05nOgYqs2DqnujSSxUhc86jbFd0E+ q6hLs5sfdrj9GIMmU/mXmO/gaNjSx4+cQOoKHg/0+H0SJzNEgKNjEDuqKNLgF6XVuIRT mahw== X-Forwarded-Encrypted: i=1; AJvYcCWGFdioonQugT2lxAsKnFaRTuWfEQSAogNB5goSDM+sgE2EsxMBY9hPHrP6+p8qUYi2heO8SNItLm3jt3E=@vger.kernel.org X-Gm-Message-State: AOJu0YyxYY0sIr1J/TJIjQNPJA3Ddfc0AGTGK6/EvFc/2h0zphnN0yWP 7a69ydIpz9Yb2XwS0ua9D3ZJl1DorUvDzPBiUFG7K9fRyFYUN/BKqG+0Wad4jtvqH9VGL6IZlcR 7CNnUDBw5dvJLHYtcCQ== X-Received: from ploe4.prod.google.com ([2002:a17:903:2404:b0:2a0:f5f5:419d]) (user=tjmercier job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:b598:b0:394:4d99:ff56 with SMTP id adf61e73a8af0-394669e12eamr341305637.11.1770933514447; Thu, 12 Feb 2026 13:58:34 -0800 (PST) Date: Thu, 12 Feb 2026 13:58:13 -0800 In-Reply-To: <20260212215814.629709-1-tjmercier@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260212215814.629709-1-tjmercier@google.com> X-Mailer: git-send-email 2.53.0.273.g2a3d683680-goog Message-ID: <20260212215814.629709-3-tjmercier@google.com> Subject: [PATCH v2 2/3] kernfs: send IN_DELETE_SELF and IN_IGNORED on file deletion From: "T.J. Mercier" To: gregkh@linuxfoundation.org, tj@kernel.org, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, shuah@kernel.org, linux-kselftest@vger.kernel.org Cc: "T.J. Mercier" Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently some kernfs files (e.g. cgroup.events, memory.events) support inotify watches for IN_MODIFY, but unlike with regular filesystems, they do not receive IN_DELETE_SELF or IN_IGNORED events when they are removed. This creates a problem for processes monitoring cgroups. For example, a service monitoring memory.events for memory.high breaches needs to know when a cgroup is removed to clean up its state. Where it's known that a cgroup is removed when all processes die, without IN_DELETE_SELF the service must resort to inefficient workarounds such as: 1. Periodically scanning procfs to detect process death (wastes CPU and is susceptible to PID reuse). 2. Placing an additional IN_DELETE watch on the parent directory (wastes resources managing double the watches). 3. Holding a pidfd for every monitored cgroup (can exhaust file descriptors). This patch enables kernfs to send IN_DELETE_SELF and IN_IGNORED events. This allows applications to rely on a single existing watch on the file of interest (e.g. memory.events) to receive notifications for both modifications and the eventual removal of the file, as well as automatic watch descriptor cleanup, simplifying userspace logic and improving resource efficiency. Implementation details: The kernfs notification worker is updated to handle file deletion. fsnotify handles sending MODIFY events to both a watched file and its parent, but it does not handle sending a DELETE event to the parent and a DELETE_SELF event to the watched file in a single call. Therefore, separate fsnotify calls are made: one for the parent (DELETE) and one for the child (DELETE_SELF), while retaining the optimized single call for MODIFY events. Signed-off-by: T.J. Mercier --- fs/kernfs/dir.c | 21 +++++++++++++++++++++ fs/kernfs/file.c | 16 ++++++++++------ fs/kernfs/kernfs-internal.h | 3 +++ 3 files changed, 34 insertions(+), 6 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 29baeeb97871..e5bda829fcb8 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -9,6 +9,7 @@ =20 #include #include +#include #include #include #include @@ -1471,6 +1472,23 @@ void kernfs_show(struct kernfs_node *kn, bool show) up_write(&root->kernfs_rwsem); } =20 +static void kernfs_notify_file_deleted(struct kernfs_node *kn) +{ + static DECLARE_WORK(kernfs_notify_deleted_work, + kernfs_notify_workfn); + + guard(spinlock_irqsave)(&kernfs_notify_lock); + /* may overwite already pending FS_MODIFY events */ + kn->attr.notify_event =3D FS_DELETE; + + if (!kn->attr.notify_next) { + kernfs_get(kn); + kn->attr.notify_next =3D kernfs_notify_list; + kernfs_notify_list =3D kn; + schedule_work(&kernfs_notify_deleted_work); + } +} + static void __kernfs_remove(struct kernfs_node *kn) { struct kernfs_node *pos, *parent; @@ -1520,6 +1538,9 @@ static void __kernfs_remove(struct kernfs_node *kn) struct kernfs_iattrs *ps_iattr =3D parent ? parent->iattr : NULL; =20 + if (kernfs_type(pos) =3D=3D KERNFS_FILE) + kernfs_notify_file_deleted(pos); + /* update timestamps on the parent */ down_write(&kernfs_root(kn)->kernfs_iattr_rwsem); =20 diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index e978284ff983..2d21af3cfcad 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -37,8 +37,8 @@ struct kernfs_open_node { */ #define KERNFS_NOTIFY_EOL ((void *)&kernfs_notify_list) =20 -static DEFINE_SPINLOCK(kernfs_notify_lock); -static struct kernfs_node *kernfs_notify_list =3D KERNFS_NOTIFY_EOL; +DEFINE_SPINLOCK(kernfs_notify_lock); +struct kernfs_node *kernfs_notify_list =3D KERNFS_NOTIFY_EOL; =20 static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node = *kn) { @@ -909,7 +909,7 @@ static loff_t kernfs_fop_llseek(struct file *file, loff= _t offset, int whence) return ret; } =20 -static void kernfs_notify_workfn(struct work_struct *work) +void kernfs_notify_workfn(struct work_struct *work) { struct kernfs_node *kn; struct kernfs_super_info *info; @@ -959,15 +959,19 @@ static void kernfs_notify_workfn(struct work_struct *= work) if (p_inode) { fsnotify(notify_event | FS_EVENT_ON_CHILD, inode, FSNOTIFY_EVENT_INODE, - p_inode, &name, inode, 0); + p_inode, &name, + (notify_event =3D=3D FS_MODIFY) ? + inode : NULL, 0); iput(p_inode); } =20 kernfs_put(parent); } =20 - if (!p_inode) - fsnotify_inode(inode, notify_event); + if (notify_event =3D=3D FS_DELETE) + fsnotify_inoderemove(inode); + else if (!p_inode) + fsnotify_inode(inode, FS_MODIFY); =20 iput(inode); } diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h index 6061b6f70d2a..cf4b21f4f3b6 100644 --- a/fs/kernfs/kernfs-internal.h +++ b/fs/kernfs/kernfs-internal.h @@ -199,6 +199,8 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node = *parent, * file.c */ extern const struct file_operations kernfs_file_fops; +extern struct kernfs_node *kernfs_notify_list; +extern void kernfs_notify_workfn(struct work_struct *work); =20 bool kernfs_should_drain_open_files(struct kernfs_node *kn); void kernfs_drain_open_files(struct kernfs_node *kn); @@ -212,4 +214,5 @@ extern const struct inode_operations kernfs_symlink_iop= s; * kernfs locks */ extern struct kernfs_global_locks *kernfs_locks; +extern spinlock_t kernfs_notify_lock; #endif /* __KERNFS_INTERNAL_H */ --=20 2.53.0.273.g2a3d683680-goog