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charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-fs-v1-18-d09a996317b3@kernel.org> References: <20261102-work-procfs-fs-v1-0-d09a996317b3@kernel.org> In-Reply-To: <20261102-work-procfs-fs-v1-0-d09a996317b3@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , Jann Horn , Josef Bacik , Chris Mason , Jeff Layton , NeilBrown , Eric Dumazet , Thomas Gleixner , Al Viro , Jonathan Corbet , Christoph Hellwig , Greg Kroah-Hartman , Joel Granados , Kees Cook , Jan Kara , Jan Kara , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-um@lists.infradead.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, ntfs3@lists.linux.dev, platform-driver-x86@vger.kernel.org, coreteam@netfilter.org, kexec@lists.infradead.org, linux-pci@vger.kernel.org, linux-sound@vger.kernel.org, netfilter-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, ibm-acpi-devel@lists.sourceforge.net, jfs-discussion@lists.sourceforge.net, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cifs@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-mm@kvack.org, linux-sh@vger.kernel.org, linux-usb@vger.kernel.org, samba-technical@lists.samba.org, sparclinux@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-doc@vger.kernel.org, linux-serial@vger.kernel.org, linux-atm-general@lists.sourceforge.net, Takashi Iwai , linux-input@vger.kernel.org, linux-raid@vger.kernel.org, linux-ext4@vger.kernel.org, linux-modules@vger.kernel.org, linux-debuggers@vger.kernel.org, "Christian Brauner (Amutable)" , Chuck Lever X-Mailer: b4 0.17-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=2074; i=brauner@kernel.org; h=from:subject:message-id; bh=tXr5cu1BdmO0jHsjps1+bZ2IKVwDVWrseoizU64SWOY=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS9WG7kztYrxVWs4L7JrPOz+wSfbxdD3doWh3h9ivDfs j/t3nS+jlIWBjEuBlkxRRaHdpNwueU8FZuNMjVg5rAygQxh4OIUgIl8TmNk2OS7Of/7mXtnrpvY SWw+cDKm06eJnev5ArnA2Z7Kmpt18xn+O605/1eW86zoiteWxTHfRDjWzEmrUjjwJ+3Hhezzqf8 qeAE= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 /proc/pressure/* are created when psi initializes and never removed. Say so with PROC_ENTRY_PERMANENT, procfs then calls into them without pinning them, like it does for /proc/profile. That also takes care of a rule the files bent. psi_write() takes the seq_file's lock to serialize the triggers. A reader holds that lock while it copies to userspace, and now that procfs owns the seq_file it does that with the entry unpinned. So nothing that runs with the entry pinned may wait for that lock, and psi_write() ran pinned. Nothing ever waited for it since the files are never removed, but with the files permanent nothing runs pinned at all. Signed-off-by: Christian Brauner (Amutable) --- kernel/sched/psi.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 3132105bf382..9811c3b705eb 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -1622,6 +1622,7 @@ static int psi_fop_release(struct inode *inode, struct file *file) } static const struct proc_ops psi_io_proc_ops = { + .proc_flags = PROC_ENTRY_PERMANENT, .proc_show = psi_io_show, .proc_write_buf = psi_io_write, .proc_poll = psi_fop_poll, @@ -1629,6 +1630,7 @@ static const struct proc_ops psi_io_proc_ops = { }; static const struct proc_ops psi_memory_proc_ops = { + .proc_flags = PROC_ENTRY_PERMANENT, .proc_show = psi_memory_show, .proc_write_buf = psi_memory_write, .proc_poll = psi_fop_poll, @@ -1636,6 +1638,7 @@ static const struct proc_ops psi_memory_proc_ops = { }; static const struct proc_ops psi_cpu_proc_ops = { + .proc_flags = PROC_ENTRY_PERMANENT, .proc_show = psi_cpu_show, .proc_write_buf = psi_cpu_write, .proc_poll = psi_fop_poll, @@ -1655,6 +1658,7 @@ static ssize_t psi_irq_write(struct file *file, char *buf, size_t nbytes, } static const struct proc_ops psi_irq_proc_ops = { + .proc_flags = PROC_ENTRY_PERMANENT, .proc_show = psi_irq_show, .proc_write_buf = psi_irq_write, .proc_poll = psi_fop_poll, -- 2.53.0