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Date: Wed, 25 Dec 2013 21:37:33 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: akpm@...ux-foundation.org, jkosina@...e.cz, joe@...ches.com,
viro@...iv.linux.org.uk, davem@...emloft.net
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] lib/vsprintf: add %pT[C012] format specifier
>>From 545dae06c6690a0c937e082ed984f828a2ea7aa2 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Wed, 25 Dec 2013 18:16:17 +0900
Subject: [PATCH] lib/vsprintf: add %pT[C012] format specifier
Since task_struct->comm can be modified by other threads while the current
thread is reading it, it is recommended to use get_task_comm() for reading it.
However, since get_task_comm() holds task_struct->alloc_lock spinlock,
some users cannot use get_task_comm(). Also, a lot of users are directly
reading from task_struct->comm even if they can use get_task_comm().
Such users might obtain inconsistent comm name.
This patch introduces %pTC format specifier for reading task_struct->comm
and %pT0 %pT1 %pT2 format specifiers for reading task_struct->comm and
task_struct->pid.
Currently %pT does not hold task_struct->alloc_lock spinlock. This is because
I'm expecting that we will change to update task_struct->comm using RCU.
By using RCU, the comm name read from task_struct->comm will be guaranteed to
be consistent. But before modifying set_task_comm() to use RCU, we need to kill
direct ->comm users who do not use get_task_comm().
Although there might be arguments that whether to modify set_task_comm() to
use RCU, this patch will anyway serve as a cleanup.
Some examples for converting direct ->comm users are shown below.
pr_info("comm=%s\n", p->comm); => pr_info("comm=%pTC\n", p);
pr_info("%s[%u]\n", p->comm, p->pid); => pr_info("%pT0\n", p);
pr_info("%s[%u]\n", p->comm, task_pid_nr(p)); => pr_info("%pT0\n", p);
pr_info("%s/%u\n", p->comm, p->pid); => pr_info("%pT1\n", p);
pr_info("%s,%u\n", p->comm, p->pid); => pr_info("%pT2\n", p);
Since many debug printings use p == current, you can pass NULL instead of p
if p == current. That is, you can simplify like examples shown below.
pr_info("comm=%s\n", current->comm); => pr_info("comm=%pTC\n", NULL);
pr_info("(%s/%u)", current->comm, current->pid); => pr_info("(%pT1)", NULL);
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
Documentation/printk-formats.txt | 12 ++++++++++
lib/vsprintf.c | 44 +++++++++++++++++++++++++++++++++++++-
2 files changed, 55 insertions(+), 1 deletions(-)
diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 445ad74..c950c04 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -177,6 +177,18 @@ dentry names:
equivalent of %s dentry->d_name.name we used to use, %pd<n> prints
n last components. %pD does the same thing for struct file.
+task_struct comm name:
+
+ format: meaning: example:
+ %pTC commname init
+ %pT0 commname[pid] init[1]
+ %pT1 commname/pid init/1
+ %pT2 commname,pid init,1
+
+ For printing task_struct->comm and optionally task_struct->pid.
+ Currently task_struct->alloc_lock is not held; might be replaced
+ by RCU in the future.
+
struct va_format:
%pV
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 10909c5..4968f57 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1155,6 +1155,38 @@ char *netdev_feature_string(char *buf, char *end, const u8 *addr,
return number(buf, end, *(const netdev_features_t *)addr, spec);
}
+static noinline_for_stack
+char *comm_name(char *buf, char *end, struct task_struct *tsk,
+ struct printf_spec spec, const char *fmt)
+{
+ char name[TASK_COMM_LEN + 20] = { };
+ const char c = *fmt;
+
+ /* Caller can pass NULL instead of current. */
+ if (!tsk)
+ tsk = current;
+ /* Not using get_task_comm() in case I'm in IRQ context. */
+ strncpy(name, tsk->comm, TASK_COMM_LEN - 1);
+ /* Optionally print pid value. */
+ if (c != 'C') {
+ struct printf_spec ps = {
+ .type = FORMAT_TYPE_UINT,
+ .base = 10,
+ };
+ char *p = name + strlen(name);
+ if (c == '0')
+ *p++ = '['; /* comm[pid] */
+ else if (c == '1')
+ *p++ = '/'; /* comm/pid */
+ else
+ *p++ = ','; /* comm,pid */
+ p = number(p, name + sizeof(name) - 2, task_pid_nr(tsk), ps);
+ if (c == '0' && p < name + sizeof(name) - 2)
+ *p++ = ']';
+ }
+ return string(buf, end, name, spec);
+}
+
int kptr_restrict __read_mostly;
/*
@@ -1221,6 +1253,7 @@ int kptr_restrict __read_mostly;
* - 'a' For a phys_addr_t type and its derivative types (passed by reference)
* - 'd[234]' For a dentry name (optionally 2-4 last components)
* - 'D[234]' Same as 'd' but for a struct file
+ * - 'T[C012]' task_struct->comm and optionally task_struct->pid
*
* Note: The difference between 'S' and 'F' is that on ia64 and ppc64
* function pointers are really function descriptors, which contain a
@@ -1232,7 +1265,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
{
int default_width = 2 * sizeof(void *) + (spec.flags & SPECIAL ? 2 : 0);
- if (!ptr && *fmt != 'K') {
+ if (!ptr && *fmt != 'K' && *fmt != 'T') {
/*
* Print (null) with the same width as a pointer so it makes
* tabular output look nice.
@@ -1364,6 +1397,15 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return dentry_name(buf, end,
((const struct file *)ptr)->f_path.dentry,
spec, fmt);
+ case 'T':
+ switch (fmt[1]) {
+ case 'C':
+ case '0':
+ case '1':
+ case '2':
+ return comm_name(buf, end, ptr, spec, fmt + 1);
+ }
+ break;
}
spec.flags |= SMALL;
if (spec.field_width == -1) {
--
1.7.1
--
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