The patch titled
Subject: proc: add some (hopefully) insightful comments
has been added to the -mm mm-nonmm-unstable branch. Its filename is
proc-add-some-hopefully-insightful-comments.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/proc-add-some-hopefully-insightful-comments.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Subject: proc: add some (hopefully) insightful comments
Date: Sat, 23 Jul 2022 20:09:07 +0300
* /proc/${pid}/net status
* removing PDE vs last close stuff (again!)
* random small stuff
Link: https://lkml.kernel.org/r/YtwrM6sDC0OQ53YB@localhost.localdomain
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/array.c | 4 ++++
fs/proc/inode.c | 17 ++++++++++++-----
fs/proc/proc_net.c | 6 ++++++
fs/proc/root.c | 5 +++++
4 files changed, 27 insertions(+), 5 deletions(-)
--- a/fs/proc/array.c~proc-add-some-hopefully-insightful-comments
+++ a/fs/proc/array.c
@@ -99,6 +99,10 @@ void proc_task_name(struct seq_file *m,
{
char tcomm[64];
+ /*
+ * Test before PF_KTHREAD because all workqueue worker threads are
+ * kernel threads.
+ */
if (p->flags & PF_WQ_WORKER)
wq_worker_comm(tcomm, sizeof(tcomm), p);
else if (p->flags & PF_KTHREAD)
--- a/fs/proc/inode.c~proc-add-some-hopefully-insightful-comments
+++ a/fs/proc/inode.c
@@ -212,7 +212,15 @@ static void unuse_pde(struct proc_dir_en
complete(pde->pde_unload_completion);
}
-/* pde is locked on entry, unlocked on exit */
+/*
+ * At most 2 contexts can enter this function: the one doing the last
+ * close on the descriptor and whoever is deleting PDE itself.
+ *
+ * First to enter calls ->proc_release hook and signals its completion
+ * to the second one which waits and then does nothing.
+ *
+ * PDE is locked on entry, unlocked on exit.
+ */
static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
__releases(&pde->pde_unload_lock)
{
@@ -222,9 +230,6 @@ static void close_pdeo(struct proc_dir_e
*
* rmmod (remove_proc_entry() et al) can't delete an entry and proceed:
* "struct file" needs to be available at the right moment.
- *
- * Therefore, first process to enter this function does ->release() and
- * signals its completion to the other process which does nothing.
*/
if (pdeo->closing) {
/* somebody else is doing that, just wait */
@@ -238,10 +243,12 @@ static void close_pdeo(struct proc_dir_e
pdeo->closing = true;
spin_unlock(&pde->pde_unload_lock);
+
file = pdeo->file;
pde->proc_ops->proc_release(file_inode(file), file);
+
spin_lock(&pde->pde_unload_lock);
- /* After ->release. */
+ /* Strictly after ->proc_release, see above. */
list_del(&pdeo->lh);
c = pdeo->c;
spin_unlock(&pde->pde_unload_lock);
--- a/fs/proc/proc_net.c~proc-add-some-hopefully-insightful-comments
+++ a/fs/proc/proc_net.c
@@ -350,6 +350,12 @@ static __net_init int proc_net_ns_init(s
kgid_t gid;
int err;
+ /*
+ * This PDE acts only as an anchor for /proc/${pid}/net hierarchy.
+ * Corresponding inode (PDE(inode) == net->proc_net) is never
+ * instantiated therefore blanket zeroing is fine.
+ * net->proc_net_stat inode is instantiated normally.
+ */
err = -ENOMEM;
netd = kmem_cache_zalloc(proc_dir_entry_cache, GFP_KERNEL);
if (!netd)
--- a/fs/proc/root.c~proc-add-some-hopefully-insightful-comments
+++ a/fs/proc/root.c
@@ -302,6 +302,11 @@ void __init proc_root_init(void)
proc_mkdir("bus", NULL);
proc_sys_init();
+ /*
+ * Last things last. It is not like userspace processes eager
+ * to open /proc files exist at this point but register last
+ * anyway.
+ */
register_filesystem(&proc_fs_type);
}
_
Patches currently in -mm which might be from adobriyan@xxxxxxxxx are
proc-add-some-hopefully-insightful-comments.patch
