Messages in this thread Patch in this message | | | Date | Fri, 9 Mar 2007 16:44:41 +0000 | From | "Catalin Marinas" <> | Subject | Re: Possible "struct pid" leak from tty_io.c |
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Eric,
For a longer explanation, see the second part of this e-mail. In short, the patch below seems to fix this particular leak. I'm not sure that's the correct/complete fix as I seem to still get a 2nd report. Any info is welcomed.
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index e453268..4e33dc2 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -1375,6 +1375,9 @@ static void do_tty_hangup(struct work_struct *work) } read_unlock(&tasklist_lock);
+ put_pid(tty->session); + put_pid(tty->pgrp); + tty->flags = 0; tty->session = NULL; tty->pgrp = NULL; On 08/03/07, Eric W. Biederman <ebiederm@xmission.com> wrote: > "Catalin Marinas" <catalin.marinas@gmail.com> writes: > > The /sbin/init application calls sys_clone() a few times but only one > > leak is reported (see below). Looking at the reported pid object (at > > 0xc7c14500), count is 2 and nr is 296 but no process with pid 296 > > exists any more. [...] > > unreferenced object 0xc7c14500 (size 36): > > comm "init", pid 245, jiffies 4294939289 > > backtrace: > > [<c0070c18>] kmem_cache_alloc > > [<c003a528>] alloc_pid > > [<c0026468>] do_fork > > [<c00153b0>] sys_clone > > [<c0010f80>] ret_fast_syscall > > I think this is the path that all pid structures come from so > unfortunately that doesn't help tracing this problem down.
No, indeed, but that's the only thing kmemleak can report. Anyway, I got some more information now, after adding several printk's:
The difference from other pid objects is that this one (with nr 296) is passed as a parameter to proc_set_tty(). The __proc_set_tty() function increments the pid->count twice via get_pid(), and, with two other get_pid calls, the pid->count for this object gets to 5 (1 being the initial value). The prints below are function name, struct pid address (different from the runs yesterday though), pid->nr and pid->count (after get_pid incrementing). It also show the return address and symbol (the calling function):
alloc_pid: c7c149d8, 296, 1 get_pid: c7c149d8, 296, 2 return: c0122d64 (proc_set_tty+0x34/0x54) get_pid: c7c149d8, 296, 3 return: c0122d64 (proc_set_tty+0x34/0x54) get_pid: c7c149d8, 296, 4 return: c002b328 (do_exit+0x2e4/0x7f8) - this is actually the get_pid in disassociate_ctty but it is reported like this because of get_pid inlining get_pid: c7c149d8, 296, 5 return: c0124a0c (tty_vhangup+0x14/0x18)
On the exit path (see below), however, put_pid is called twice before free_pid and once via release_task -> detach_pid -> free_pid -> ... -> __rcu_process_callbacks -> delayed_put_pid -> put_pid. Note that free_pid is called with pid->nr == 3 and the last put_pid gets called with nr == 3 as well (but it decrements it to 2 and that's what I find at that memory location). In the trace below, the pid->count is printed before put_pid modifies it:
put_pid: c7c149d8, 296, 5 return: c0124b5c (disassociate_ctty+0x14c/0x230) put_pid: c7c149d8, 296, 4 return: c0124ba8 (disassociate_ctty+0x198/0x230) detach_pid: c7c149d8, 296, 3 return: c002a230 (release_task+0x1c0/0x358) detach_pid: c7c149d8, 296, 3 return: c002a248 (release_task+0x1d8/0x358) detach_pid: c7c149d8, 296, 3 return: c002a254 (release_task+0x1e4/0x358) free_pid: c7c149d8, 296, 3 return: c003a990 (detach_pid+0xac/0xc8) ... delayed_put_pid: c7c149d8, 296, 3 return: c003af68 (__rcu_process_callbacks+0x19c/0x25c) put_pid: c7c149d8, 296, 3 return: c003a8cc (delayed_put_pid+0x54/0x6c)
In the above disassociate_ctty() function the code below (line 1542) doesn't seem to get called:
tty = get_current_tty(); if (tty) { put_pid(tty->session); put_pid(tty->pgrp); tty->session = NULL; tty->pgrp = NULL; } else { and I get the following error if TTY_DEBUG_HANGUP is defined - "error attempted to write to tty [0x00000000] = NULL". It looks like the tty_vhangup() call in in disassociate_ctty() sets current->signal->tty to NULL in the do_each_pid_task loop in do_tty_hangup (p->signal->tty = NULL). The second call to get_current_tty() in disassociate_ctty() return NULL and therefore no put_pid on tty->session and tty->pgrp (which are also set to NULL in the previous function).
Regards.
-- Catalin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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