Re: 2.6.24-rc2-mm1: kcryptd vs lockdep

Re: 2.6.24-rc2-mm1: kcryptd vs lockdep

[Oleg Nesterov]

Alasdair G Kergon wrote:
>
>   - But what happens if kcryptd_crypt_write_convert_loop() calls
> INIT_WORK/queue_work twice?

Can't find this function. But "INIT_WORK + queue_work" twice is very
wrong of course.

Milan Broz wrote:
>
> Ok, then I have question: Is the following pseudocode correct
> (and problem is in lock validation which checks something
> already initialized for another queue) or reusing work_struct
> is not permitted from inside called work function ?
>
> (Note comment in code "It is permissible to free the struct
> work_struct from inside the function that is called from it".)
>
> struct work_struct work;
> struct workqueue_struct *a, *b;
>
> do_b(*work)
> {
>         /* do something else */
> }
>
> do_a(*work)
> {
>         /* do something */
>         INIT_WORK(&work, do_b);
>         queue_work(b, &work);
> }
>
>
> INIT_WORK(&work, do_a);
> queue_work(a, &work);

(just in case, in that particular case PREPARE_WORK() should be used)

INIT_WORK(w) can be used if we know that "w" is not pending, and nobody
else can write to this work (say, queue_work(w) or cancel_work_sync(w)).
So currently the code above should work correctly.

However, I'd say it is not correct, INIT_WORK() can throw out some debug
info for example, or the implementation could be changed.

I'm not sure about CONFIG_LOCKDEP (Johannes cc'ed). INIT_WORK() does
lockdep_init_map(->lockdep_map) but run_workqueue() has a local copy,
looks ok.

Oleg.

Re: 2.6.24-rc2-mm1: kcryptd vs lockdep

[Johannes Berg]

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Hi,

> > Ok, then I have question: Is the following pseudocode correct
> > (and problem is in lock validation which checks something
> > already initialized for another queue) or reusing work_struct
> > is not permitted from inside called work function ?
> >
> > (Note comment in code "It is permissible to free the struct
> > work_struct from inside the function that is called from it".)
> >
> > struct work_struct work;
> > struct workqueue_struct *a, *b;
> >
> > do_b(*work)
> > {
> >         /* do something else */
> > }
> >
> > do_a(*work)
> > {
> >         /* do something */
> >         INIT_WORK(&work, do_b);
> >         queue_work(b, &work);
> > }
> >
> >
> > INIT_WORK(&work, do_a);
> > queue_work(a, &work);
> 
> (just in case, in that particular case PREPARE_WORK() should be used)
> 
> INIT_WORK(w) can be used if we know that "w" is not pending, and nobody
> else can write to this work (say, queue_work(w) or cancel_work_sync(w)).
> So currently the code above should work correctly.
> 
> However, I'd say it is not correct, INIT_WORK() can throw out some debug
> info for example, or the implementation could be changed.
> 
> I'm not sure about CONFIG_LOCKDEP (Johannes cc'ed). INIT_WORK() does
> lockdep_init_map(->lockdep_map) but run_workqueue() has a local copy,
> looks ok.

We explicitly need to use a copy of the lockdep_map for "locking" the
work struct as per the quoted comment. So as far as I can tell, what
INIT_WORK() is doing here is changing an at that point unused copy of
the lockdep map so I think it should be fine. Not sure about the other
fine points nor why you'd want this though :)

johannes

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[PATCH] debug_check_no_locks_freed: fix in_range() checks

[Oleg Nesterov]

Torsten, could you ack/nack this patch?

Torsten Kaiser wrote:
>
> static inline int in_range(const void *start, const void *addr, const void *end)
> {
>         return addr >= start && addr <= end;
> }
> This  will return true, if addr is in the range of start (including)
> to end (including).
>
> But debug_check_no_locks_freed() seems does:
> const void *mem_to = mem_from + mem_len
> -> mem_to is the last byte of the freed range, that fits in_range
> lock_from = (void *)hlock->instance;
> -> first byte of the lock
> lock_to = (void *)(hlock->instance + 1);
> -> first byte of the next lock, not last byte of the lock that is being checked!
>
> The test is:
> if (!in_range(mem_from, lock_from, mem_to) &&
>                                         !in_range(mem_from, lock_to, mem_to))
>                         continue;
> So it tests, if the first byte of the lock is in the range that is freed ->OK
> And if the first byte of the *next* lock is in the range that is freed
> -> Not OK.

We can also simplify in_range checks, we need only 2 comparisons, not 4.
If the lock is not in memory range, it should be either at the left of range
or at the right.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 24/kernel/lockdep.c~	2007-11-09 12:57:31.000000000 +0300
+++ 24/kernel/lockdep.c	2007-11-24 13:32:52.000000000 +0300
@@ -3054,11 +3054,6 @@ void __init lockdep_info(void)
 #endif
 }
 
-static inline int in_range(const void *start, const void *addr, const void *end)
-{
-	return addr >= start && addr <= end;
-}
-
 static void
 print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
 		     const void *mem_to, struct held_lock *hlock)
@@ -3080,6 +3075,13 @@ print_freed_lock_bug(struct task_struct 
 	dump_stack();
 }
 
+static inline int not_in_range(const void* mem_from, unsigned long mem_len,
+				const void* lock_from, unsigned long lock_len)
+{
+	return lock_from + lock_len <= mem_from ||
+		mem_from + mem_len <= lock_from;
+}
+
 /*
  * Called when kernel memory is freed (or unmapped), or if a lock
  * is destroyed or reinitialized - this code checks whether there is
@@ -3087,7 +3089,6 @@ print_freed_lock_bug(struct task_struct 
  */
 void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
 {
-	const void *mem_to = mem_from + mem_len, *lock_from, *lock_to;
 	struct task_struct *curr = current;
 	struct held_lock *hlock;
 	unsigned long flags;
@@ -3100,14 +3101,11 @@ void debug_check_no_locks_freed(const vo
 	for (i = 0; i < curr->lockdep_depth; i++) {
 		hlock = curr->held_locks + i;
 
-		lock_from = (void *)hlock->instance;
-		lock_to = (void *)(hlock->instance + 1);
-
-		if (!in_range(mem_from, lock_from, mem_to) &&
-					!in_range(mem_from, lock_to, mem_to))
+		if (not_in_range(mem_from, mem_len, hlock->instance,
+					sizeof(*hlock->instance)))
 			continue;
 
-		print_freed_lock_bug(curr, mem_from, mem_to, hlock);
+		print_freed_lock_bug(curr, mem_from, mem_from + mem_len, hlock);
 		break;
 	}
 	local_irq_restore(flags);

Re: [PATCH] debug_check_no_locks_freed: fix in_range() checks

[Torsten Kaiser]

On Nov 24, 2007 11:53 AM, Oleg Nesterov <oleg@tv-sign.ru> wrote:
> Torsten, could you ack/nack this patch?

>From looking at the code I would ack it.
I will reapply agk-dm-dm-crypt-move-bio-submission-to-thread.patch and
this patch and boot several times, but as the message was not
triggered on every boot, this can't prove anything.

But if it happens again, I will notify you.

Torsten

> Torsten Kaiser wrote:
> >
> > static inline int in_range(const void *start, const void *addr, const void *end)
> > {
> >         return addr >= start && addr <= end;
> > }
> > This  will return true, if addr is in the range of start (including)
> > to end (including).
> >
> > But debug_check_no_locks_freed() seems does:
> > const void *mem_to = mem_from + mem_len
> > -> mem_to is the last byte of the freed range, that fits in_range
> > lock_from = (void *)hlock->instance;
> > -> first byte of the lock
> > lock_to = (void *)(hlock->instance + 1);
> > -> first byte of the next lock, not last byte of the lock that is being checked!
> >
> > The test is:
> > if (!in_range(mem_from, lock_from, mem_to) &&
> >                                         !in_range(mem_from, lock_to, mem_to))
> >                         continue;
> > So it tests, if the first byte of the lock is in the range that is freed ->OK
> > And if the first byte of the *next* lock is in the range that is freed
> > -> Not OK.
>
> We can also simplify in_range checks, we need only 2 comparisons, not 4.
> If the lock is not in memory range, it should be either at the left of range
> or at the right.
>
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
>
> --- 24/kernel/lockdep.c~        2007-11-09 12:57:31.000000000 +0300
> +++ 24/kernel/lockdep.c 2007-11-24 13:32:52.000000000 +0300
> @@ -3054,11 +3054,6 @@ void __init lockdep_info(void)
>  #endif
>  }
>
> -static inline int in_range(const void *start, const void *addr, const void *end)
> -{
> -       return addr >= start && addr <= end;
> -}
> -
>  static void
>  print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
>                      const void *mem_to, struct held_lock *hlock)
> @@ -3080,6 +3075,13 @@ print_freed_lock_bug(struct task_struct
>         dump_stack();
>  }
>
> +static inline int not_in_range(const void* mem_from, unsigned long mem_len,
> +                               const void* lock_from, unsigned long lock_len)
> +{
> +       return lock_from + lock_len <= mem_from ||
> +               mem_from + mem_len <= lock_from;
> +}
> +
>  /*
>   * Called when kernel memory is freed (or unmapped), or if a lock
>   * is destroyed or reinitialized - this code checks whether there is
> @@ -3087,7 +3089,6 @@ print_freed_lock_bug(struct task_struct
>   */
>  void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
>  {
> -       const void *mem_to = mem_from + mem_len, *lock_from, *lock_to;
>         struct task_struct *curr = current;
>         struct held_lock *hlock;
>         unsigned long flags;
> @@ -3100,14 +3101,11 @@ void debug_check_no_locks_freed(const vo
>         for (i = 0; i < curr->lockdep_depth; i++) {
>                 hlock = curr->held_locks + i;
>
> -               lock_from = (void *)hlock->instance;
> -               lock_to = (void *)(hlock->instance + 1);
> -
> -               if (!in_range(mem_from, lock_from, mem_to) &&
> -                                       !in_range(mem_from, lock_to, mem_to))
> +               if (not_in_range(mem_from, mem_len, hlock->instance,
> +                                       sizeof(*hlock->instance)))
>                         continue;
>
> -               print_freed_lock_bug(curr, mem_from, mem_to, hlock);
> +               print_freed_lock_bug(curr, mem_from, mem_from + mem_len, hlock);
>                 break;
>         }
>         local_irq_restore(flags);
>
>

Re: [PATCH] debug_check_no_locks_freed: fix in_range() checks

[Ingo Molnar]

* Oleg Nesterov <oleg@tv-sign.ru> wrote:

> > But debug_check_no_locks_freed() seems does:
> > const void *mem_to = mem_from + mem_len
> > -> mem_to is the last byte of the freed range, that fits in_range
> > lock_from = (void *)hlock->instance;
> > -> first byte of the lock
> > lock_to = (void *)(hlock->instance + 1);
> > -> first byte of the next lock, not last byte of the lock that is being checked!
> >
> > The test is:
> > if (!in_range(mem_from, lock_from, mem_to) &&
> >                                         !in_range(mem_from, lock_to, mem_to))
> >                         continue;
> > So it tests, if the first byte of the lock is in the range that is freed ->OK
> > And if the first byte of the *next* lock is in the range that is freed
> > -> Not OK.

thanks, applied.

	Ingo

Re: [PATCH] debug_check_no_locks_freed: fix in_range() checks

[Oleg Nesterov]

On 11/24, Torsten Kaiser wrote:
>
> On Nov 24, 2007 11:53 AM, Oleg Nesterov <oleg@tv-sign.ru> wrote:
> > Torsten, could you ack/nack this patch?
> 
> From looking at the code I would ack it.

Great.

> I will reapply agk-dm-dm-crypt-move-bio-submission-to-thread.patch and
> this patch and boot several times, but as the message was not
> triggered on every boot, this can't prove anything.

Regardless of any other possible problems, I think you found a real bug
in debug_check_no_locks_freed() which should be fixed.

Oleg.

Re: [PATCH] debug_check_no_locks_freed: fix in_range() checks

[Alasdair G Kergon]

On Sat, Nov 24, 2007 at 01:18:35PM +0100, Torsten Kaiser wrote:
> I will reapply agk-dm-dm-crypt-move-bio-submission-to-thread.patch and
> this patch and boot several times

OK for a test system, but until the write loop problem is addressed I believe
there's a risk of data corruption under low memory conditions.  (I dropped it
from the export to -mm a few days ago for this reason.)

Alasdair
-- 
agk@redhat.com