| Message ID | 20250331121820.455916-2-bhupesh@igalia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Dynamically allocate memory to store task's full name | expand |
On Mon, Mar 31, 2025 at 8:18 PM Bhupesh <bhupesh@igalia.com> 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@igalia.com> > --- > 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); > + 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; > + Adding another field to store the task name isn’t ideal. What about combining them into a single field, as Linus suggested [0]? [0]. https://lore.kernel.org/all/CAHk-=wjAmmHUg6vho1KjzQi2=psR30+CogFd4aXrThr2gsiS4g@mail.gmail.com/
On Mon, Mar 31, 2025 at 05:48:18PM +0530, Bhupesh 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@igalia.com> > --- > 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); > + if (!name) > + return -ENOMEM; Is it safe to return error here, instead of jumping to 'out_unlock' label and then releasing locks? > + 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 > >
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); + 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) {
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@igalia.com> --- fs/exec.c | 21 ++++++++++++++++++--- include/linux/sched.h | 9 +++++++++ 2 files changed, 27 insertions(+), 3 deletions(-)