Top 10 kernel oopses for the week ending January 5th, 2008

The http://www.kerneloops.org website collects kernel oops and warning reports from various mailing lists and bugzillas as well as with a client users can install to auto-submit oopses. Below is a top 10 list of the oopses collected in the last 7 days. (Reports prior to 2.6.23 have been omitted in collecting the top 10)

This week, a total of 49 oopses and warnings have been reported, compared to 53 reports in the previous week.

Rank 1: __ieee80211_rx
Warning at net/mac80211/rx.c:1672
Reported 6 times (11 total reports)
Same issue that was ranked 2nd last week
Johannes has diagnosed this as a driver bug in the iwlwifi drivers More info: http://www.kerneloops.org/search.php?search=__ieee80211_rx

Rank 2: elv_next_request
kernel page fault
Reported 6 times (7 total reports)
Seems to be related to fast modprobe/rmmod cycles
More info: http://www.kerneloops.org/search.php?search=elv_next_request

Rank 3: d_splice_alias
NULL pointer deref
Reported 3 times
Happens in the isofs code
Only seen in 2.6.24-rc5-mm1
More info: http://www.kerneloops.org/search.php?search=d_splice_alias

Rank 4: remove_proc_entry
Was also ranked 4th last week
Only in tainted oopses
Reported 3 times (12 total reports)
More info: http://www.kerneloops.org/search.php?search=remove_proc_entry

Rank 5: __d_path
In the sys_getcwd system call
Only reported for 2.6.23.x, by one user
Reported 2 times
More info: http://www.kerneloops.org/search.php?search=__d_path

Rank 6: device_release
Was ranked 8th last week
Same reports as last week, but now entered into bugzilla.kernel.org Reported 2 times (8 total reports)
More info: http://www.kerneloops.org/search.php?search=device_release

Rank 7: pgd_alloc
Has only been seen on machines tainted with the nvidia module Reported 2 times
More info: http://www.kerneloops.org/search.php?search=pgd_alloc

Rank 8: evdev_disconnect
kernel page fault
Reported 2 times (10 total reports)
Previously seen in older kernels including 2.6.21 but as far back as 2.6.16 More info: http://www.kerneloops.org/search.php?search=evdev_disconnect

Rank 9: mutex_lock
kernel null pointer due to rfcomm_tty_close sysfs interaction Reported 2 times (9 total reports)
Ranked 9th last week as well
More info: http://www.kerneloops.org/search.php?search=mutex_lock

Rank 10: lock_acquire

	WARNING: at kernel/lockdep.c:2658 check_flags()
	Reported 2 times (8 total reports)
	Seems related to __atomic_notifier_call_chain
	More info: http://www.kerneloops.org/search.php?search=lock_acquire

kerneloops.org news
* There is now a UI client so that if your kernel has an oops, you'll get asked for permission to submit this (rather than having to manually edit a config file as before)
* If you run the Gentoo distribution, please install the client using "emerge kerneloops"
* If you run the Fedora 8 (or rawhide) distribution, please install the rpm you can download from the http://www.kerneloops.org homepage
* If you run Debian unstable, please install the client via apt-get install kerneloops

in -rc6-mm1 as well, fixes on l-k...

Practically certain to be fixed by 6addb1d6de1968b84852f54561cc9a999909b5a9; it's list_for_each_entry() walking from the entry that just got list_del() and kernels without that sucker have no protection of the list in question whatsoever.

pissfs locking problems; AFAICS, its sysfs_get_dentry() walking into already unlinked sysfs directory node on the way to target; no exclusion against that is there and it's not trivial to add.

FWIW, people moaning about the lack of entry-level kernel work would do well by decoding those to the level of "this place in this function, called from <here>, with so-and-so variable being <this>" and posting the results. As skills go, it's far more useful than "how to trim the trailing whitespace" and the rest of checkpatch.pl-inspired crap that got so popular lately...

Likely a broken module_exit() function that corrupts the list. To track these down it might be useful to keep a list of recently unloaded modules and dump these too in the oops module list with a special flag.

-Andi

I suspect that simply printing the currently unloading module will catch 90%+ already; I'll look into adding this, it's a very good idea.

There are a few cases where the corruption is only visible next time someone accesses the list. So a small ring buffer might make sense.

-Andi

Is there any good basic documentation on this to point people at?

--b.

I would second this question. I see people "decode" oops on lkml often enough, but I've never been entirely sure how its done. Is it somewhere in Documentation?

Kevin Winchester

It's actually not necessarily at all that trivial, unless you have a deep understanding of the code generated for the architecture in question (and even then, some oopses take more time to figure out than others, thanks to inlining and tailcalls etc).

If the oops happened with a kernel you generated yourself, it's usually rather easy. Especially if you said "y" to the "generate debugging info" question at configuration time. Because, in that case, you really just do a simple

gdb vmlinux

and then you can do (for example) something like setting a breakpoint at the EIP that was reported for the oops, and it will tell you what line it came from.

However, if you don't have the exact binary - which is the common case for random oopses reported on lkml - you will generally have to disassemble the hex sequence given in the oops (the "Code:" line), and try to match it up against the source code to try to figure out what is going on.

Even just the disassembly is not entirely trivial, since the oops will give you the eip that it happened at, but you often want to also disassemble *backwards* in order to get more of a context (the "Code:" line will mark the particular EIP that starts the oopsing instruction by enclosing it in <xx>, but with non-constant instruction lengths, you need to use a bit of trial-and-error to figure it out.

I usually just compile a small program like

	const char array[]="\xnn\xnn\xnn...";

	int main(int argc, char **argv)
	{
		printf("%p\n", array);
		*(int *)0=0;
	}

and run it under gdb, and then when it gets the SIGSEGV (due to the obvious NULL pointer dereference), I can just ask gdb to disassemble around the array that contains the code[] stuff. Try a few offsets, to see when the disassembly makes sense (and gives the reported EIP as the beginning of one of the disassembled instructions).

(You can do it other and smarter ways too, I'm not claiming that's a particularly good way to do it, and the old "ksymoops" program used to do a pretty good job of this, but I'm used to that particular idiotic way myself, since it's how I've basically always done it)

After that, you still need to try to match up the assembly code with the source code and figure out what variables the register contents actually are all about. You can often try to do a

make the/affected/file.s

to generate the asm file in your own tree - the register allocation can be totally different due to different compilers and different options (and things like the fact that maybe the source tree you do this on doesn't match the oops report exactly), but it's usually a good starting point to compare the disassembly from gdb with the *.s file output from the compiler.

Quite often, it's all very obvious (you see some constant or other simple pattern). But if you're not used to the assembly format, you'll spend a lot of brainpower just trying to figure that part out even for the obvious stuff, which is why it's a good thing if you are very comfortable indeed with the assembly language of that particular platform.

It's not really all that hard. But the first few times you see those oopses, it all looks mostly like just line noise. So it definitely takes some practice to do it well.

Anyway, let's take an example, from

	http://lkml.org/lkml/2008/1/1/189

where the most obviously relevant parts are:

	BUG: unable to handle kernel paging request at virtual address 00100100
	EIP:    0060:[<f8819668>] 
	EIP is at evdev_disconnect+0x65/0x9e

	eax: 00000000   ebx: 000ffcf0   ecx: c1926760   edx: 00000033
	esi: f7415600   edi: f741564c   ebp: f7415654   esp: c1967e68
	Call Trace:
		[<c03454b2>] input_unregister_device+0x6f/0xff
		[<c03c6eb6>] klist_release+0x27/0x30
		[<c029178a>] kref_put+0x5f/0x6c
	..
	Code: 5e 4c 81 eb 10 04 00 00 eb 21 8d 83 08 04 00 00 b9 06 00 02 
	      00 ba 1d 00 00 00 e8 6a 93 95 c7 8b 9b 10 04 00 00 81 eb 10 
	      04 00 00 <8b> 83 10 04 00 00 0f 18 00 90 8d 83 10 04 00 00 
	      39 f8 75 cb 8d

so here let's do the above silly C program:

	const char array[]="\x5e\x4c\x81\xeb\x10\x04\x00\x00\xeb\x21..

and running it under gdb gives:

	0x8048500

	Program received signal SIGSEGV, Segmentation fault.
	0x080483f7 in main () at test.c:14
	14              *(int*)0=0;

and now I can just try

	x/20i 0x8048500

and it turns out that already gives a reasonable disassembly. The first few instructions are bogus: they're really part of the previous instruction, but it looks pretty sane around the actual problem spot, which is "array+43" (there are 42 bytes of code before the EIP one, and 20 bytes after):

	0x8048500 <array>:      pop    %esi
	0x8048501 <array+1>:    dec    %esp
	0x8048502 <array+2>:    sub    $0x410,%ebx
	0x8048508 <array+8>:    jmp    0x804852b <array+43>
	0x804850a <array+10>:   lea    0x408(%ebx),%eax
	0x8048510 <array+16>:   mov    $0x20006,%ecx
	0x8048515 <array+21>:   mov    $0x1d,%edx
	0x804851a <array+26>:   call   0xcf9a1889
	0x804851f <array+31>:   mov    0x410(%ebx),%ebx
	0x8048525 <array+37>:   sub    $0x410,%ebx
	0x804852b <array+43>:   mov    0x410(%ebx),%eax
	0x8048531 <array+49>:   prefetchnta (%eax)
	0x8048534 <array+52>:   nop
	0x8048535 <array+53>:   lea    0x410(%ebx),%eax
	0x804853b <array+59>:   cmp    %edi,%eax
	0x804853d <array+61>:   jne    0x804850a <array+10>
	0x804853f <array+63>:   lea    (%eax),%eax
	.. 

so now we know that the faulting instruction was that

	mov    0x410(%ebx),%eax

and we can also see that this also matches the address that caused the oops (ebx=000ffcf0, so 0x410(%ebx) is 00100100, which matches the "unable to handle kernel paging request" message).

(Now, people used to kernel oopses will also recognize 00100100 as the LIST_POISON1, so this is all about dereferencing the ->next pointer of a list entry that has been removed from the list, but that's a whole separate level of kernel knowledge).

Anyway, you can now do

make drivers/input/evdev.s

and see if you can find that kind of code sequence in there. You can use the "EIP: evdev_disconnect+0x65/0x9e" thing as a hint: if your compiler setup isn't too different, it's likely to be roughly two thirds into that evdev_disconnect function (but inlining really can mean that it's somewhere else entirely in the source tree!)

The rest left as an exercise for the reader.

Linus

Heh. I prefer
char main[] = {.....};
for the same thing, with gdb a.out and no running at all.

FWIW, I'm going to go through Arjan's collection and post blow-by-blow analysis of some of those suckers. Tonight, probably...

Let's take e.g. http://www.kerneloops.org/raw.php?rawid=2618

RIP: 0010:[<ffffffff803b49a1>]  [<ffffffff803b49a1>] kref_put+0x31/0x80
RSP: 0000:ffff81007ffe5df0  EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000034333545 RCX: ffffffff80606270
RDX: 0000000000000040 RSI: ffffffff803b38b0 RDI: 0000000034333545
RBP: ffff81007ffe5e00 R08: 0000000000000001 R09: 0000000000000000
R10: ffffffff8094c430 R11: 0000000000000000 R12: ffffffff803b38b0
R13: ffff81011ede44d8 R14: ffffffff804d7d50 R15: ffff81011ff210f0
FS:  0000000002024870(0000) GS:ffff81011ff0dd00(0000)
...
Call Trace:
 [<ffffffff803b37e9>] kobject_put+0x19/0x20
 [<ffffffff803b389b>] kobject_del+0x2b/0x40
 [<ffffffff804d7d50>] delayed_delete+0x0/0xb0
 [<ffffffff804d7db9>] delayed_delete+0x69/0xb0
 [<ffffffff80249775>] run_workqueue+0x175/0x210
 [<ffffffff8024a411>] worker_thread+0x71/0xb0
 [<ffffffff8024d9e0>] autoremove_wake_function+0x0/0x40
 [<ffffffff8024a3a0>] worker_thread+0x0/0xb0
 [<ffffffff8024d5fd>] kthread+0x4d/0x80
 [<ffffffff8020c4b8>] child_rip+0xa/0x12
 [<ffffffff8020bbcf>] restore_args+0x0/0x30
 [<ffffffff8024d5b0>] kthread+0x0/0x80
 [<ffffffff8020c4ae>] child_rip+0x0/0x12

Code: f0 ff 0b 0f 94 c0 31 d2 84 c0 74 0b 48 89 df 41 ff d4 ba 01

What do we have here? It barfs in kref_put() called from kobject_put(). It's -rc6-mm1 and I don't have -mm at hand. Let's see if we can make any sense out of it from the mainline - it might be a good idea for the first pass, unless there are some clear indications to the contrary.

kref_put() is fairly low-level (and deep in call chain, here). And it's pretty small:
int kref_put(struct kref *kref, void (*release)(struct kref *kref))

{
        WARN_ON(release == NULL);
        WARN_ON(release == (void (*)(struct kref *))kfree);

        if (atomic_dec_and_test(&kref->refcount)) {
                release(kref);
                return 1;
        }
        return 0;
}

Poking around on the site (I'm not familiar enough with it, so bear with me) gives a link to posting and an important detail missed in that page:

<1>Unable to handle kernel paging request at 0000000034333545 RIP:
[<ffffffff803b49a1>] kref_put+0x31/0x80

Now, that's interesting - we barf on dereferencing a pointer that (a) has upper 32 bits zero and (b) doesn't have a bit 7 set in any byte. Smells like ASCII data misinterpreted as a pointer. Conversion to ASCII gives "E534", which sure as hell does look like a fragment of some string.

OK, so where does that happen? In this case we have only one candidate, really - atomic_dec_and_test(&kref->refcount). Before it we only compare argument with constants, after it we pass argument to another function.

Now, looking at the registers (see above) we notice that this address had come from rbx. Let's try objdump -d lib/kref.o and see what we've got there for kref_put():

  4a:   55                      push   %rbp
  4b:   48 85 f6                test   %rsi,%rsi
  4e:   48 c7 c1 00 00 00 00    mov    $0x0,%rcx
  55:   ba 36 00 00 00          mov    $0x36,%edx
  5a:   48 89 e5                mov    %rsp,%rbp
  5d:   41 54                   push   %r12
  5f:   49 89 f4                mov    %rsi,%r12
  62:   53                      push   %rbx
  63:   48 89 fb                mov    %rdi,%rbx
  66:   74 15                   je     7d <kref_put+0x33>
  68:   48 81 fe 00 00 00 00    cmp    $0x0,%rsi
  6f:   75 26                   jne    97 <kref_put+0x4d>
  71:   48 c7 c1 00 00 00 00    mov    $0x0,%rcx
  78:   ba 37 00 00 00          mov    $0x37,%edx
  7d:   48 c7 c6 00 00 00 00    mov    $0x0,%rsi
  84:   48 c7 c7 00 00 00 00    mov    $0x0,%rdi
  8b:   31 c0                   xor    %eax,%eax
  8d:   e8 00 00 00 00          callq  92 <kref_put+0x48>
  92:   e8 00 00 00 00          callq  97 <kref_put+0x4d>
  97:   f0 ff 0b                lock decl (%rbx)
  9a:   0f 94 c0                sete   %al
  9d:   31 d2                   xor    %edx,%edx
  9f:   84 c0                   test   %al,%al
  a1:   74 0b                   je     ae <kref_put+0x64>
  a3:   48 89 df                mov    %rbx,%rdi
  a6:   41 ff d4                callq  *%r12
  a9:   ba 01 00 00 00          mov    $0x1,%edx
  ae:   5b                      pop    %rbx
  af:   41 5c                   pop    %r12
  b1:   c9                      leaveq 
  b2:   89 d0                   mov    %edx,%eax
  b4:   c3                      retq   

It's not necessary identical to what that kernel had; still, not bad for a starting point. We are even lucky enough to find 'f0 ff' immediately in there:
97: f0 ff 0b lock decl (%rbx)
Next instructions also match - actually, better than I expected. So. We even have register allocation matching the reported kernel and it all makes sense - this is the instruction where it had puked, the address had, indeed, come from rbx and it's locked decrement of *rbx followed by some testing and conditional jump. Just what one would expect from atomic_dec_and_test().

IOW, we have &kref->refcount equal to 0x0000000034333545. What's the value of kref itself? We could look into definition of struct kref, or just notice that release(kref) should be right after that, so we could see what gets passed to it.

  a3:   48 89 df                mov    %rbx,%rdi
  a6:   41 ff d4                callq  *%r12

is clearly it. So what we are passing is rbx itself, so that offset got to be zero.

All right, so we have kref_put() getting 0x0000000034333545 instead of a pointer in the first argument. It's called from kobject_put() and unless -mm has changes in there, there's no need to guess where in kobject_put() that had been:
void kobject_put(struct kobject * kobj)

{
        if (kobj)
                kref_put(&kobj->kref, kobject_release);
}

Aha. Now, we need to work back from &kobj->kref to kobj. Again, assuming that -mm doesn't change struct kobject in a way that would affect the offset, we have

struct kobject {
        const char              * k_name;
        struct kref             kref;
        struct list_head        entry;

...
Looks like it's not too likely, unless somebody had been deliberately rearranging fields (to fit cachelines better, etc.). We'll need to verify that, of course, but for now it's a good starting assumption. Very well, we have one pointer in front of it. It's an amd64, so it's an 8 byte field and no alignment padding is to be expected. IOW, kobj is 0x0000000034333545 - 8, i.e. 0x000000003433353D. What's _that_ in ASCII? "=534". OK, that makes even more sense for a part of some string...

Let's check; time to take a look at that patch, after all
struct kobject {

-       const char              * k_name;
+       const char              *name;
        struct kref             kref;

OK, not a problem. While we are at it, kobject_put() is unchanged by the patch. Now, back to trace. kobject_put() is called from kobject_del(). Now, that one does differ from mainline:

void kobject_del(struct kobject * kobj)

{
	if (!kobj)
		return;

	sysfs_remove_dir(kobj);
	kobj->state_in_sysfs = 0;
	kobj_kset_leave(kobj);
	kobject_put(kobj->parent);
	kobj->parent = NULL;
}

Humm... So we have kobj->parent containing crap. What about the caller? It's from drivers/md/md.c:
static void delayed_delete(struct work_struct *ws)

{
        mdk_rdev_t *rdev = container_of(ws, mdk_rdev_t, del_work);
        kobject_del(&rdev->kobj);
}
and it's only used in
static void unbind_rdev_from_array(mdk_rdev_t * rdev)
{
        char b[BDEVNAME_SIZE];
        if (!rdev->mddev) {
                MD_BUG();
                return;
        }
        bd_release_from_disk(rdev->bdev, rdev->mddev->gendisk);
        list_del_init(&rdev->same_set);
        printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));
        rdev->mddev = NULL;
        sysfs_remove_link(&rdev->kobj, "block");

        /* We need to delay this, otherwise we can deadlock when
         * writing to 'remove' to "dev/state"
         */
        INIT_WORK(&rdev->del_work, delayed_delete);
        schedule_work(&rdev->del_work);
}

Well, that takes care of the rest of trace - we have used INIT_WORK to set rdev->del_work up, scheduled it for execution and eventually the callback had been called (asynchronously to us).

So what do we have so far?

	unbind_rdev_from_array(rdev);

had been called and rdev->kobj.parent turned to contain a crap value (0x000000003433353D) instead of a pointer. That's about all we can get out of trace.

Now, let's see what could have triggered it. Curious... Looking through diff shows an interesting bit:

-       rdev->kobj.parent = &mddev->kobj;
-       if ((err = kobject_add(&rdev->kobj)))
+       if ((err = kobject_add(&rdev->kobj, &mddev->kobj, "dev-%s", b)))
                goto fail;

in bind_rdev_to_array(). At the first sight the changes in kobject_add() seem to match that. And nothing else in md.c seems to be setting it to anything non-NULL. Very well, so it's one of the following:

* unbind_rdev_from_array() called on rdev that didn't pass through
bind_rdev_to_array().
* unbind_rdev_from_array() called on rdev that bailed out from
bind_rdev_to_array() before that point.
* mddev value in the above is crap. That's bloody unlikely, BTW -
kobject_add() would increment the refcount of rdev->kobj.parent (or we would be in far more trouble, since it would not match kobject_del() and _that_ would hurt a lot more than just md.c). So &mddev->kobj would better be something saner when it went through that point.
* *rdev got corrupted in between.

Actually, looking at the callers of unbind_rdev_from_array()... We always follow it with export_rdev(). Which does (presumably) final kobject_put() on &rdev->kobj, freeing rdev itself.

What guarantees that it doesn't happen before we get to callback? AFAICS, nothing whatsoever...

And if it does happen, we'll get rdev happily freed (by rdev_free(), as ->release() of &rdev->kobj) by the time we get to delayed_delete(). Which explains what's going on just fine.

BTW, -mm changes in kobject.c explain WTF it doesn't trigger in mainline - there we managed to get away with that since kobject_add() bumped refcount of kobject by one and kobject_del() decremented it. That masked the bug.

...

IMHO, it would be really wasteful if Arian havn't published these and maybe a few more such advices and links on this site, not necessarily waiting for html-ized or howto-ized versions!

Thanks,
Jarek P.

One other way to do it (at least for x86-32/64) is to use $kerneltree/scripts/decodecode. It may work on other $arches also, but I haven't tested it on others.

---
~Randy

Just use scripts/decodecode and cat the Code line into that.

IMHO better is

make the/file/xyz.lst

which gives you a listing with binary data in there which can be grepped for.

But you should install a very recent binutils because older objdump -S couldn't deal with unit-at-a-time compilers.

-Andi

I've made life easier for those using the www.kerneloops.org website; at least for x86 oopses the website now does this for you and shows the decoded Code: line in the raw oops data:

http://www.kerneloops.org/raw.php?rawid=2716

Cool.

One thing I wonder about - could you separate out the bug-ons and warnings from the oopses? They really are different issues, and an oops with register information etc is very different from a BUG() with line numbers, which in turn is very different from a WARN_ON().

Right now, it says

	Oopses reported for kernel 2.6.24-rc7


	7 oopses reported

	hfsplus_releasepage	3
	enqueue_task		1
	lock_acquire		1
	__hfs_brec_find		1
	__ieee80211_rx		1

and in fact three of those five entries are really WARN_ON's. It would be nicer if it would look more along the lines of

Backtraces reported for kernel 2.6.24-rc7

4 oopses reported

hfsplus_releasepage 3
__hfs_brec_find 1

3 warnings repored

enqueue_task 1
lock_acquire 1
__ieee80211_rx 1

because those things really don't have the same kind of impact at all, and tend to be very different to debug (a "BUG_ON()" is perhaps somewhat closer to an oops, but a WARN_ON() is definitely in a class of its own).

On that "Code:" side, it seems there is still some problem with oops parsing. See for example:

	http://www.kerneloops.org/raw.php?rawid=1521&msgid=http://mid.gmane.org/[email protected]

and notice how the Code: never made it into the raw message (and thus there is also no instruction disassembly).

Linus

the database has the information so it's just a matter of slightly different php code ;) Before I do that... do you want the BUG's separate, part of the warnings or part of the oopses? (I rather make this change once ;)

ok I'll fix this; I can fix this for all new entries at least, fixing retroactive is going to be near impossible I suspect.

I'd like them all separate, they tend to be very different and contain different information.

Put the warnings last, as the least important. Oopses at the top, since they tend to be the ones that are less expected.

Oh well..

Linus

ok done; I had to fizzle a bit because some things aren't *exactly* a BUG() statement but I track them anyway (things like the "sleeping in invalid context" check), so I had to somewhat arbitrarily assign categories for those. I might fine tune these over time some; if you or someone else sees problems with categorization please let me know

Looking good. I wonder if we could also have some way to cross-ref these things with the regression list (notably try to get pointers to them in the regression list).

Right now, the regression list keeps track of the things that are closed, but kerneloops.org obviously doesn't see that, so it's not obvious which oopses are "uninteresting" since they've been fixed.

Linus

I'm thinking about that, but haven't invented any automated solution yet. I only can manually add references to kerneloops.org, for now.

Greetings,
Rafael

Note that because we don't get the module list for WARN_ON, we don't actually know whether all of these instances are from the iwlwifi drivers. A few other drivers suffer from the same problem. In one of these cases, iwlwifi was contained in the stack trace, but in the common case that isn't happening because packet processing is delayed to a tasklet.

johannes

and fwiw a patch to get this added to WARN_ON was posted by my last week to fix this; once this goes into 2.6.25-rc this annoyance/hinderance in debugging will be fixed.

Thanks for that analysis.
...

This is a good argument for sticking "md_" at the from of all my function names, even if they are static. I'm fairly sure I looked at that trace:

but as it doesn't mention 'md' or 'nfs' I moved on. My bad.

Yes, that's bad isn't it :-)

I think I should be using sysfs_schedule_callback here. That makes the required 'get' and 'put' calls.... but it can fail with -ENOMEM. I wonder what I do if -ENOMEM??? Maybe I'll just continue to roll my one :-(

Thanks,
NeilBrown

How about this instead (completely untested)

* split failure exits
* switch to kick_rdev_from_array()
* fold unbind_rdev_from_array() into it (no other callers anymore)
* take export_rdev() into failure case in bind_rdev_to_array()
* in kick_rdev_from_array() do what export_rdev() does sans
kobject_put() and do that before schedule_work(). Take kobject_put() into delayed_delete().

---

index cef9ebd..116cc5a 100644
@@ -1344,6 +1344,39 @@ static int match_mddev_units(mddev_t *mddev1, mddev_t *mddev2)
 
 static LIST_HEAD(pending_raid_disks);
 
+static void unlock_rdev(mdk_rdev_t *rdev)
+{
+	struct block_device *bdev = rdev->bdev;
+	rdev->bdev = NULL;
+	if (!bdev)
+		MD_BUG();
+	bd_release(bdev);
+	blkdev_put(bdev);
+}
+
+void md_autodetect_dev(dev_t dev);
+
+static void __export_rdev(mdk_rdev_t * rdev)
+{
+	char b[BDEVNAME_SIZE];
+	printk(KERN_INFO "md: export_rdev(%s)\n",
+		bdevname(rdev->bdev,b));
+	if (rdev->mddev)
+		MD_BUG();
+	free_disk_sb(rdev);
+	list_del_init(&rdev->same_set);
+#ifndef MODULE
+	md_autodetect_dev(rdev->bdev->bd_dev);
+#endif
+	unlock_rdev(rdev);
+}
+
+static void export_rdev(mdk_rdev_t * rdev)
+{
+	__export_rdev(rdev);
+	kobject_put(&rdev->kobj);
+}
+
 static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 {
 	char b[BDEVNAME_SIZE];

@@ -1353,7 +1386,8 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 
 	if (rdev->mddev) {
 		MD_BUG();
-		return -EINVAL;
+		err = -EINVAL;
+		goto out;
 	}
 	/* make sure rdev->size exceeds mddev->size */
 	if (rdev->size && (mddev->size == 0 || rdev->size < mddev->size)) {

@@ -1362,8 +1396,10 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 			 * If mddev->level <= 0, then we don't care
 			 * about aligning sizes (e.g. linear)
 			 */
-			if (mddev->level > 0)
-				return -ENOSPC;
+			if (mddev->level > 0) {
+				err = -ENOSPC;
+				goto out;
+			}
 		} else
 			mddev->size = rdev->size;
 	}

@@ -1379,12 +1415,16 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 			choice++;
 		rdev->desc_nr = choice;
 	} else {
-		if (find_rdev_nr(mddev, rdev->desc_nr))
-			return -EBUSY;
+		if (find_rdev_nr(mddev, rdev->desc_nr)) {
+			err = -EBUSY;
+			goto out;
+		}
 	}
 	bdevname(rdev->bdev,b);
-	if (kobject_set_name(&rdev->kobj, "dev-%s", b) < 0)
-		return -ENOMEM;
+	if (kobject_set_name(&rdev->kobj, "dev-%s", b) < 0) {
+		err = -ENOMEM;
+		goto out;
+	}
 	while ( (s=strchr(rdev->kobj.k_name, '/')) != NULL)
 		*s = '!';
 			

@@ -1407,9 +1447,11 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 	bd_claim_by_disk(rdev->bdev, rdev, mddev->gendisk);
 	return 0;
 
- fail:
+fail:
 	printk(KERN_WARNING "md: failed to register dev-%s for %s\n",
 	       b, mdname(mddev));
+out:
+	export_rdev(rdev);
 	return err;
 }
 

@@ -1417,19 +1459,22 @@ static void delayed_delete(struct work_struct *ws)
 {
 	mdk_rdev_t *rdev = container_of(ws, mdk_rdev_t, del_work);
 	kobject_del(&rdev->kobj);
+	kobject_put(&rdev->kobj);
 }
 
-static void unbind_rdev_from_array(mdk_rdev_t * rdev)
+static void kick_rdev_from_array(mdk_rdev_t * rdev)
 {
 	char b[BDEVNAME_SIZE];
 	if (!rdev->mddev) {
 		MD_BUG();
+		export_rdev(rdev);
 		return;
 	}
 	bd_release_from_disk(rdev->bdev, rdev->mddev->gendisk);
 	list_del_init(&rdev->same_set);
 	printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));
 	rdev->mddev = NULL;
+	__export_rdev(rdev);
 	sysfs_remove_link(&rdev->kobj, "block");
 
 	/* We need to delay this, otherwise we can deadlock when

@@ -1467,40 +1512,6 @@ static int lock_rdev(mdk_rdev_t *rdev, dev_t dev)
 	return err;
 }
 
-static void unlock_rdev(mdk_rdev_t *rdev)
-{
-	struct block_device *bdev = rdev->bdev;
-	rdev->bdev = NULL;
-	if (!bdev)
-		MD_BUG();
-	bd_release(bdev);
-	blkdev_put(bdev);
-}
-
-void md_autodetect_dev(dev_t dev);
-
-static void export_rdev(mdk_rdev_t * rdev)
-{
-	char b[BDEVNAME_SIZE];
-	printk(KERN_INFO "md: export_rdev(%s)\n",
-		bdevname(rdev->bdev,b));
-	if (rdev->mddev)
-		MD_BUG();
-	free_disk_sb(rdev);
-	list_del_init(&rdev->same_set);
-#ifndef MODULE
-	md_autodetect_dev(rdev->bdev->bd_dev);
-#endif
-	unlock_rdev(rdev);
-	kobject_put(&rdev->kobj);
-}
-
-static void kick_rdev_from_array(mdk_rdev_t * rdev)
-{
-	unbind_rdev_from_array(rdev);
-	export_rdev(rdev);
-}
-
 static void export_array(mddev_t *mddev)
 {
 	struct list_head *tmp;

@@ -2576,8 +2587,10 @@ new_dev_store(mddev_t *mddev, const char *buf, size_t len)
 						       mdk_rdev_t, same_set);
 			err = super_types[mddev->major_version]
 				.load_super(rdev, rdev0, mddev->minor_version);
-			if (err < 0)
-				goto out;
+			if (err < 0) {
+				export_rdev(rdev);
+				return err;
+			}
 		}
 	} else
 		rdev = md_import_device(dev, -1, -1);

@@ -2585,9 +2598,6 @@ new_dev_store(mddev_t *mddev, const char *buf, size_t len)
 	if (IS_ERR(rdev))
 		return PTR_ERR(rdev);
 	err = bind_rdev_to_array(rdev, mddev);
- out:
-	if (err)
-		export_rdev(rdev);
 	return err ? err : len;
 }
 

@@ -3637,8 +3647,7 @@ static void autorun_devices(int part)
 			printk(KERN_INFO "md: created %s\n", mdname(mddev));
 			ITERATE_RDEV_GENERIC(candidates,rdev,tmp) {
 				list_del_init(&rdev->same_set);
-				if (bind_rdev_to_array(rdev, mddev))
-					export_rdev(rdev);
+				bind_rdev_to_array(rdev, mddev);
 			}
 			autorun_array(mddev);
 			mddev_unlock(mddev);

@@ -3807,7 +3816,6 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
 		return -EOVERFLOW;
 
 	if (!mddev->raid_disks) {
-		int err;
 		/* expecting a device which has a superblock */
 		rdev = md_import_device(dev, mddev->major_version, mddev->minor_version);
 		if (IS_ERR(rdev)) {

@@ -3830,10 +3838,7 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
 				return -EINVAL;
 			}
 		}
-		err = bind_rdev_to_array(rdev, mddev);
-		if (err)
-			export_rdev(rdev);
-		return err;
+		return bind_rdev_to_array(rdev, mddev);
 	}
 
 	/*

@@ -3887,10 +3892,8 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
 				validate_super(mddev, rdev);
 			err = mddev->pers->hot_add_disk(mddev, rdev);
 			if (err)
-				unbind_rdev_from_array(rdev);
+				kick_rdev_from_array(rdev);
 		}
-		if (err)
-			export_rdev(rdev);
 
 		md_update_sb(mddev, 1);
 		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);

@@ -3908,7 +3911,6 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
 	}
 
 	if (!(info->state & (1<<MD_DISK_FAULTY))) {
-		int err;
 		rdev = md_import_device (dev, -1, 0);
 		if (IS_ERR(rdev)) {
 			printk(KERN_WARNING 

@@ -3938,11 +3940,7 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info)
 			rdev->sb_offset = calc_dev_sboffset(rdev->bdev);
 		rdev->size = calc_dev_size(rdev, mddev->chunk_size);
 
-		err = bind_rdev_to_array(rdev, mddev);
-		if (err) {
-			export_rdev(rdev);
-			return err;
-		}
+		return bind_rdev_to_array(rdev, mddev);
 	}
 
 	return 0;

@@ -4018,15 +4016,15 @@ static int hot_add_disk(mddev_t * mddev, dev_t dev)
 		printk(KERN_WARNING 
 			"md: can not hot-add faulty %s disk to %s!\n",
 			bdevname(rdev->bdev,b), mdname(mddev));
-		err = -EINVAL;
-		goto abort_export;
+		export_rdev(rdev);
+		return -EINVAL;
 	}
 	clear_bit(In_sync, &rdev->flags);
 	rdev->desc_nr = -1;
 	rdev->saved_raid_disk = -1;
 	err = bind_rdev_to_array(rdev, mddev);
 	if (err)
-		goto abort_export;
+		return err;
 
 	/*
 	 * The rest should better be atomic, we can have disk failures

@@ -4036,8 +4034,8 @@ static int hot_add_disk(mddev_t * mddev, dev_t dev)
 	if (rdev->desc_nr == mddev->max_disks) {
 		printk(KERN_WARNING "%s: can not hot-add to full array!\n",
 			mdname(mddev));
-		err = -EBUSY;
-		goto abort_unbind_export;
+		kick_rdev_from_array(rdev);
+		return -EBUSY;
 	}
 
 	rdev->raid_disk = -1;

@@ -4052,13 +4050,6 @@ static int hot_add_disk(mddev_t * mddev, dev_t dev)
 	md_wakeup_thread(mddev->thread);
 	md_new_event(mddev);
 	return 0;
-
-abort_unbind_export:
-	unbind_rdev_from_array(rdev);

While there are probably some good ideas in there, I think fixing this particular bug is much simpler. Just take a reference to the object before scheduling the worker, and drop it when the worker has done its work.

I have a closer look at the idea of no required export_rdev after a failed bind_rdev_to_array. On the surface it does seem to make the code nicer.

Thanks,
NeilBrown