Messages in this thread Patch in this message | | | Subject | [PATCH] lib/vsprintf: add %pT[C012] format specifier | From | Tetsuo Handa <> | Date | Wed, 25 Dec 2013 21:37:33 +0900 |
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>From 545dae06c6690a0c937e082ed984f828a2ea7aa2 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa <penguin-kernel@I-love.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@I-love.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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