From a71ad98c580b910d2fe92e358cabafa9e6df275a Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Thu, 22 May 2014 10:43:37 +1000 Subject: [PATCH] lib/vsprintf: add %pT 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 result. This patch introduces %pT format specifier for printing task_struct->comm. Currently %pT does not provide consistency. I'm planning to change to use RCU in the future. 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(). An example for converting direct ->comm users is shown below. Since many debug printings use p == current, you can pass NULL instead of p if p == current. pr_info("comm=%s\n", p->comm); => pr_info("comm=%pT\n", p); pr_info("comm=%s\n", current->comm); => pr_info("comm=%pT\n", NULL); Signed-off-by: Tetsuo Handa Reviewed-by: Pavel Machek Reviewed-by: Kees Cook Signed-off-by: Andrew Morton --- Documentation/printk-formats.txt | 6 ++++++ lib/vsprintf.c | 20 +++++++++++++++++++- 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt index 6f4eb322ffaf..94459b42e0ab 100644 --- a/Documentation/printk-formats.txt +++ b/Documentation/printk-formats.txt @@ -184,6 +184,12 @@ dentry names: equivalent of %s dentry->d_name.name we used to use, %pd prints n last components. %pD does the same thing for struct file. +task_struct comm name: + + %pT + + For printing task_struct->comm. + struct va_format: %pV diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 0648291cdafe..e30d885d9631 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1183,6 +1183,21 @@ char *address_val(char *buf, char *end, const void *addr, return number(buf, end, num, 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]; + + /* Caller can pass NULL instead of current. */ + if (!tsk) + tsk = current; + /* Not using get_task_comm() in case I'm in IRQ context. */ + memcpy(name, tsk->comm, TASK_COMM_LEN); + name[sizeof(name) - 1] = '\0'; + return string(buf, end, name, spec); +} + int kptr_restrict __read_mostly; /* @@ -1250,6 +1265,7 @@ int kptr_restrict __read_mostly; * (default assumed to be phys_addr_t, 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' task_struct->comm * * Note: The difference between 'S' and 'F' is that on ia64 and ppc64 * function pointers are really function descriptors, which contain a @@ -1261,7 +1277,7 @@ 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. @@ -1389,6 +1405,8 @@ 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': + return comm_name(buf, end, ptr, spec, fmt); } spec.flags |= SMALL; if (spec.field_width == -1) { -- 2.39.5