On 4/3/25 9:47 PM, Andrii Nakryiko wrote:
On Mon, Mar 31, 2025 at 5:18 AM Bhupesh <bhupesh@xxxxxxxxxx> wrote:Provide a parallel implementation for get_task_comm() called get_task_full_name() which allows the dynamically allocated and filled-in task's full name to be passed to interested users such as 'gdb'. Currently while running 'gdb', the 'task->comm' value of a long task name is truncated due to the limitation of TASK_COMM_LEN. For example using gdb to debug a simple app currently which generate threads with long task names: # gdb ./threadnames -ex "run info thread" -ex "detach" -ex "quit" > log # cat log NameThatIsTooLo This patch does not touch 'TASK_COMM_LEN' at all, i.e. 'TASK_COMM_LEN' and the 16-byte design remains untouched. Which means that all the legacy / existing ABI, continue to work as before using '/proc/$pid/task/$tid/comm'. This patch only adds a parallel, dynamically-allocated 'task->full_name' which can be used by interested users via '/proc/$pid/task/$tid/full_name'. After this change, gdb is able to show full name of the task: # gdb ./threadnames -ex "run info thread" -ex "detach" -ex "quit" > log # cat log NameThatIsTooLongForComm[4662] Signed-off-by: Bhupesh <bhupesh@xxxxxxxxxx> --- fs/exec.c | 21 ++++++++++++++++++--- include/linux/sched.h | 9 +++++++++ 2 files changed, 27 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index f45859ad13ac..4219d77a519c 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1208,6 +1208,9 @@ int begin_new_exec(struct linux_binprm * bprm) { struct task_struct *me = current; int retval; + va_list args; + char *name; + const char *fmt; /* Once we are committed compute the creds */ retval = bprm_creds_from_file(bprm); @@ -1348,11 +1351,22 @@ int begin_new_exec(struct linux_binprm * bprm) * detecting a concurrent rename and just want a terminated name. */ rcu_read_lock(); - __set_task_comm(me, smp_load_acquire(&bprm->file->f_path.dentry->d_name.name), - true); + fmt = smp_load_acquire(&bprm->file->f_path.dentry->d_name.name); + name = kvasprintf(GFP_KERNEL, fmt, args);this `args` argument, it's not initialized anywhere, right? It's not clear where it's coming from, but you are passing it directly into kvasprintf(), I can't convince myself that this is correct. Can you please explain what is happening here? Also, instead of allocating a buffer unconditionally, maybe check that comm is longer than 16, and if not, just use the old-schoold 16-byte comm array?
Ok. As Kees also mentioned in his comment, I will try to do away with the allocation in the exec() hot-path in v3.
+ if (!name) + return -ENOMEM; + + me->full_name = name; + __set_task_comm(me, fmt, true); rcu_read_unlock(); } else { - __set_task_comm(me, kbasename(bprm->filename), true); + fmt = kbasename(bprm->filename); + name = kvasprintf(GFP_KERNEL, fmt, args); + if (!name) + return -ENOMEM; + + me->full_name = name; + __set_task_comm(me, fmt, true); } /* An exec changes our domain. We are no longer part of the thread @@ -1399,6 +1413,7 @@ int begin_new_exec(struct linux_binprm * bprm) return 0; out_unlock: + kfree(me->full_name); up_write(&me->signal->exec_update_lock); if (!bprm->cred) mutex_unlock(&me->signal->cred_guard_mutex); diff --git a/include/linux/sched.h b/include/linux/sched.h index 56ddeb37b5cd..053b52606652 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1166,6 +1166,9 @@ struct task_struct { */ char comm[TASK_COMM_LEN]; + /* To store the full name if task comm is truncated. */ + char *full_name; + struct nameidata *nameidata; #ifdef CONFIG_SYSVIPC @@ -2007,6 +2010,12 @@ extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec buf; \ }) +#define get_task_full_name(buf, buf_size, tsk) ({ \ + BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \ + strscpy_pad(buf, (tsk)->full_name, buf_size); \ + buf; \ +}) + #ifdef CONFIG_SMP static __always_inline void scheduler_ipi(void) { -- 2.38.1
Thanks.
