Messages in this thread Patch in this message | | | Date | Thu, 5 Jun 2008 19:23:16 +0400 | From | Oleg Nesterov <> | Subject | TASK_WAKEKILL && /sbin/init (was: [PATCH 1/2] schedule: fix TASK_WAKEKILL vs SIGKILL race) |
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Sorry Matthew, I left this part unanswered because I didn't have the time yesterday...
On 06/04, Matthew Wilcox wrote: > > On Wed, Jun 04, 2008 at 09:09:05PM +0400, Oleg Nesterov wrote: > > Note also that with or without this patch TASK_WAKEKILL is not exactly right > > wrt /sbin/init, but this is another issue. > > That's certainly an interesting conversation to have.
If lock_page_killable() fails because the task was killed by SIGKILL or another fatal signal, do_generic_file_read() returns -EIO.
This seems to be OK, because in fact the userspace won't see this error, the task will dequeue SIGKILL and exit.
However, /sbin/init is different, it will dequeue SIGKILL, ignore it, and be confused by this bogus -EIO. Please note that while this bug is not likely, it is _not_ theoretical. It does happen that user-space sends the unhandled fatal signals to init.
Imho, this is 2.6.26 material. Unless I missed something, of course.
It is not clear to me what should we do. I'd like very much to avoid adding more SIGNAL_UNKILLABLE checks, but perhaps we don't have another choice. We can fix the bug with
--- kernel/signal.c +++ kernel/signal.c @@ -974,7 +974,7 @@ void zap_other_threads(struct task_struc int fastcall __fatal_signal_pending(struct task_struct *tsk) { - return sigismember(&tsk->pending.signal, SIGKILL); + return signal_group_exit(tsk->signal); }
, but this makes __fatal_signal_pending() slower, and because we use tsk->signal, schedule() (in particular) can't use this helper.
Anyway. How about the (untested/uncompiled) patch for now? -EINTR or -ERESTARTNOINTR looks "more correct" regardless.
Oleg.
--- mm/filemap.c +++ mm/filemap.c @@ -188,7 +188,7 @@ static int sync_page(void *word) static int sync_page_killable(void *word) { sync_page(word); - return fatal_signal_pending(current) ? -EINTR : 0; + return fatal_signal_pending(current) ? -ERESTARTNOINTR : 0; } /** @@ -1000,8 +1000,9 @@ page_ok: page_not_up_to_date: /* Get exclusive access to the page ... */ - if (lock_page_killable(page)) - goto readpage_eio; + error = lock_page_killable(page); + if (error) + goto readpage_error; /* Did it get truncated before we got the lock? */ if (!page->mapping) { @@ -1029,8 +1030,9 @@ readpage: } if (!PageUptodate(page)) { - if (lock_page_killable(page)) - goto readpage_eio; + error = lock_page_killable(page); + if (error) + goto readpage_error; if (!PageUptodate(page)) { if (page->mapping == NULL) { /*
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