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SubjectBug in find_task_by_pid()? (was Re: /proc/non-existent-pid/)
Hi,

This (in 2.1.128) is because find_task_by_pid() returns a valid task
structure for a process that already exited. This lasts for a few seconds
and then eventually disappears. If you put a printk() after the line
p = find_task_by_pid(pid) in fs/proc/fd.c/proc_readfd() you will see it for
yourself. So, either read_lock(&task_list) does not work or something
is wrong with the way find_task_by_pid() manipulates the pid hashtable.

Someone please narrow it down further.

Regards,
Tigran

On Thu, 12 Nov 1998, Koblinger Egmont wrote:

>
> Hi folks!
>
> Several weeks ago I reported a bug. No answer came, and the bug is still
> present in 2.1.127. :-( So I send the report again.
>
> It's possible that an entry remains in the proc fs after the command has
> exited. It seems to me that it happens if we run an `ls -l' command in the
> /proc/$pid/fd directory while the command runs. After command exits, `ls
> /proc' does not write its pid, but /proc/$pid still exists.
> See the log file at the end of the message.
>
> Two more questions about /proc/$pid/fd:
> 1. Instead of 64, could the "correct" length of the symlinks be returned?
> 2. When a file is deleted, the string "/tmp/x (deleted)" could rather be
> "deleted:/tmp/x". This is because it's more similar to the pipe: and
> socket: ones, and a normal file _can_ have the name "/tmp/x (deleted)"
> so it cannot be told whether this really means a deleted file. On the
> other hand, "deleted:/tmp/x" can not be the full name of a real file.
> So it would be more simplier and more consequent to parse the
> "deleted:/tmp/x" notation within a program.
>
> Bye
> Egmont Koblinger
> <egmont@math.bme.hu>
>
>
> Here is the log file how I can invoke the bug:
> egmont $ sleep 10 &
> [1] 182
> egmont $ ls -l /proc/182/fd
> total 0
> lrwx------ 1 egmont pupil 64 Oct 20 20:50 0 -> /dev/ttyp0
> lrwx------ 1 egmont pupil 64 Oct 20 20:50 1 -> /dev/ttyp0
> lrwx------ 1 egmont pupil 64 Oct 20 20:50 2 -> /dev/ttyp0
> egmont $ ##### wait ten seconds
> [1]+ Done sleep 10
> egmont $ ls /proc | grep 182
> egmont $ ls -l /proc/182
> ls: /proc/182/exe: Permission denied
> ls: /proc/182/root: Permission denied
> ls: /proc/182/cwd: Permission denied
> total 0
> -r--r--r-- 1 root root 0 Oct 20 20:50 cmdline
> -r--r--r-- 1 root root 0 Oct 20 20:50 cpu
> lrwx------ 1 root root 0 Oct 20 20:50 cwd
> -r-------- 1 root root 0 Oct 20 20:50 environ
> lrwx------ 1 root root 0 Oct 20 20:50 exe
> dr-x------ 2 egmont pupil 0 Oct 20 20:50 fd
> pr--r--r-- 1 root root 0 Oct 20 20:50 maps
> -rw------- 1 root root 0 Oct 20 20:50 mem
> lrwx------ 1 root root 0 Oct 20 20:50 root
> -r--r--r-- 1 root root 0 Oct 20 20:50 stat
> -r--r--r-- 1 root root 0 Oct 20 20:50 statm
> -r--r--r-- 1 root root 0 Oct 20 20:50 status
> egmont $ ##### well, that's it
>
>
>
>
>
> -
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