On 12/11/20 3:01 PM, Jonathan Lemon wrote:
On Fri, Dec 11, 2020 at 12:23:34PM -0800, Andrii Nakryiko wrote:
@@ -164,7 +164,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
curr_files = get_files_struct(curr_task);
if (!curr_files) {
put_task_struct(curr_task);
- curr_tid = ++(info->tid);
+ curr_tid = curr_tid + 1;
Yonghong might know definitively, but it seems like we need to update
info->tid here as well:
info->tid = curr_tid;
If the search eventually yields no task, then info->tid will stay at
some potentially much smaller value, and we'll keep re-searching tasks
from the same TID on each subsequent read (if user keeps reading the
file). So corner case, but good to have covered.
That applies earlier as well:
curr_task = task_seq_get_next(ns, &curr_tid, true);
if (!curr_task) {
info->task = NULL;
info->files = NULL;
return NULL;
}
The logic seems to be "if task == NULL, then return NULL and stop".
Is the seq_iterator allowed to continue/restart if seq_next returns NULL?
If seq_next() returns NULL, bpf_seq_read() will end and the control
will return to user space. There are two cases here:
- there are something in the buffer and user will get non-zero-length
return data and after this typically user will call read() syscall
again. In such cases case, the search will be from last info->tid.
- the buffer is empty and user will get a "0" return value for read()
system. Typically, user will not call read() syscall any more.
But if it does, the search will start from last info->tid.
Agree with Andrii, in general, this should not be a big problem.
But it is good to get this fixed too.
--
Jonathan
