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Message-Id: <20230414052840.1994456-3-mcgrof@kernel.org>
Date: Thu, 13 Apr 2023 22:28:40 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: david@...hat.com, patches@...ts.linux.dev,
linux-modules@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, pmladek@...e.com,
petr.pavlu@...e.com, prarit@...hat.com,
torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
rafael@...nel.org
Cc: christophe.leroy@...roup.eu, tglx@...utronix.de,
peterz@...radead.org, song@...nel.org, rppt@...nel.org,
dave@...olabs.net, willy@...radead.org, vbabka@...e.cz,
mhocko@...e.com, dave.hansen@...ux.intel.com,
colin.i.king@...il.com, jim.cromie@...il.com,
catalin.marinas@....com, jbaron@...mai.com,
rick.p.edgecombe@...el.com, mcgrof@...nel.org
Subject: [RFC 2/2] kread: avoid duplicates
With this we run into 0 wasted virtual memory bytes.
Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---
fs/kernel_read_file.c | 150 ++++++++++++++++++++++++++++++++++++++++++
kernel/module/main.c | 6 +-
2 files changed, 154 insertions(+), 2 deletions(-)
diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index 5d826274570c..209c56764442 100644
--- a/fs/kernel_read_file.c
+++ b/fs/kernel_read_file.c
@@ -4,6 +4,7 @@
#include <linux/kernel_read_file.h>
#include <linux/security.h>
#include <linux/vmalloc.h>
+#include <linux/fdtable.h>
/**
* kernel_read_file() - read file contents into a kernel buffer
@@ -171,17 +172,166 @@ ssize_t kernel_read_file_from_path_initns(const char *path, loff_t offset,
}
EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
+DEFINE_MUTEX(kread_dup_mutex);
+static LIST_HEAD(kread_dup_reqs);
+
+struct kread_dup_req {
+ struct list_head list;
+ char name[PATH_MAX];
+ struct completion first_req_done;
+ struct work_struct complete_work;
+ struct delayed_work delete_work;
+ int dup_ret;
+};
+
+static struct kread_dup_req *kread_dup_request_lookup(char *name)
+{
+ struct kread_dup_req *kread_req;
+
+ list_for_each_entry_rcu(kread_req, &kread_dup_reqs, list,
+ lockdep_is_held(&kread_dup_mutex)) {
+ if (strlen(kread_req->name) == strlen(name) &&
+ !memcmp(kread_req->name, name, strlen(name))) {
+ return kread_req;
+ }
+ }
+
+ return NULL;
+}
+
+static void kread_dup_request_delete(struct work_struct *work)
+{
+ struct kread_dup_req *kread_req;
+ kread_req = container_of(to_delayed_work(work), struct kread_dup_req, delete_work);
+
+ mutex_lock(&kread_dup_mutex);
+ list_del_rcu(&kread_req->list);
+ synchronize_rcu();
+ mutex_unlock(&kread_dup_mutex);
+ kfree(kread_req);
+}
+
+static void kread_dup_request_complete(struct work_struct *work)
+{
+ struct kread_dup_req *kread_req;
+
+ kread_req = container_of(work, struct kread_dup_req, complete_work);
+
+ complete_all(&kread_req->first_req_done);
+ queue_delayed_work(system_wq, &kread_req->delete_work, 60 * HZ);
+}
+
+static bool kread_dup_request_exists_wait(char *name, int *dup_ret)
+{
+ struct kread_dup_req *kread_req, *new_kread_req;
+ int ret;
+
+ /*
+ * Pre-allocate the entry in case we have to use it later
+ * to avoid contention with the mutex.
+ */
+ new_kread_req = kzalloc(sizeof(*new_kread_req), GFP_KERNEL);
+ if (!new_kread_req)
+ return false;
+
+ memcpy(new_kread_req->name, name, strlen(name));
+ INIT_WORK(&new_kread_req->complete_work, kread_dup_request_complete);
+ INIT_DELAYED_WORK(&new_kread_req->delete_work, kread_dup_request_delete);
+ init_completion(&new_kread_req->first_req_done);
+
+ mutex_lock(&kread_dup_mutex);
+
+ kread_req = kread_dup_request_lookup(name);
+ if (!kread_req) {
+ /*
+ * There was no duplicate, just add the request so we can
+ * keep tab on duplicates later.
+ */
+ //pr_info("New kread request for %s\n", name);
+ list_add_rcu(&new_kread_req->list, &kread_dup_reqs);
+ mutex_unlock(&kread_dup_mutex);
+ return false;
+ }
+ mutex_unlock(&kread_dup_mutex);
+
+ /* We are dealing with a duplicate request now */
+
+ kfree(new_kread_req);
+
+ //pr_warn("kread: duplicate request for file %s\n", name);
+
+ ret = wait_for_completion_state(&kread_req->first_req_done,
+ TASK_UNINTERRUPTIBLE | TASK_KILLABLE);
+ if (ret) {
+ *dup_ret = ret;
+ return true;
+ }
+
+ /* breath */
+ schedule_timeout(2*HZ);
+
+ *dup_ret = kread_req->dup_ret;
+
+ return true;
+}
+
+void kread_dup_request_announce(char *name, int ret)
+{
+ struct kread_dup_req *kread_req;
+
+ mutex_lock(&kread_dup_mutex);
+
+ kread_req = kread_dup_request_lookup(name);
+ if (!kread_req)
+ goto out;
+
+ kread_req->dup_ret = ret;
+
+ /*
+ * If we complete() here we may allow duplicate threads
+ * to continue before the first one that submitted the
+ * request. We're in no rush but avoid boot delays caused
+ * by these threads waiting too long.
+ */
+ queue_work(system_wq, &kread_req->complete_work);
+
+out:
+ mutex_unlock(&kread_dup_mutex);
+}
+
ssize_t kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
size_t buf_size, size_t *file_size,
enum kernel_read_file_id id)
{
struct fd f = fdget(fd);
ssize_t ret = -EBADF;
+ char *name, *path;
+ int dup_ret;
if (!f.file || !(f.file->f_mode & FMODE_READ))
goto out;
+ path = kzalloc(PATH_MAX, GFP_KERNEL);
+ if (!path)
+ return -ENOMEM;
+
+ name = file_path(f.file, path, PATH_MAX);
+ if (IS_ERR(name)) {
+ ret = PTR_ERR(name);
+ goto out_mem;
+ }
+
+ if (kread_dup_request_exists_wait(name, &dup_ret)) {
+ ret = -EBUSY;
+ goto out_mem;
+ }
+
ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id);
+
+ kread_dup_request_announce(name, ret);
+
+out_mem:
+ kfree(path);
out:
fdput(f);
return ret;
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 1ed373145278..e99419b4d85c 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -3080,8 +3080,10 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
len = kernel_read_file_from_fd(fd, 0, &buf, INT_MAX, NULL,
READING_MODULE);
if (len < 0) {
- mod_stat_inc(&failed_kreads);
- mod_stat_add_long(len, &invalid_kread_bytes);
+ if (len != -EBUSY) {
+ mod_stat_inc(&failed_kreads);
+ mod_stat_add_long(len, &invalid_kread_bytes);
+ }
return len;
}
--
2.39.2
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