* oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) [not found] ` <20031208222526.GA31134@kroah.com> @ 2003-12-08 22:48 ` Greg KH 2003-12-08 22:58 ` Greg KH 2003-12-28 12:38 ` Andrey Borzenkov 0 siblings, 2 replies; 6+ messages in thread From: Greg KH @ 2003-12-08 22:48 UTC (permalink / raw) To: Andrew Morton, maneesh, mgorse, linux-kernel Cc: Andrey Borzenkov, Patrick Mochel Ok, I'm ccing lkml and everyone else who has been in on this thread at different times. This is based on a patch from Andrey that was/is in the -mm tree for a while. On Mon, Dec 08, 2003 at 02:25:26PM -0800, Greg KH wrote: > On Thu, Oct 09, 2003 at 01:48:37AM -0700, Andrew Morton wrote: > > > > I've had this in -mm for a while. What to do with it? > > Heh, nothing like digging up something from the past that I insisted was > not needed, but... > > > It is possible that parent is removed before child when child is in use. > > Trivial example is mounted USB storage when you unplug it. The kobject for > > USB device is removed but subordinate SCSI device remains. Then kernel oopses > > on attempt to release child e.g. umount removed USB storage. This patch fixes > > two problems: > > Yes, I now think this patch needs to be applied. I can easily cause a > parent device in sysfs to go away, with the child still present: > - plug in a usb-serial device > - run 'cat /dev/ttyUSB0' > - yank the device out. > Now if you cancel the 'cat' program, lovely oopses... > > So, Andrew, very sorry about this, but this patch should be sent to > Linus. I think Pat agrees with me, but he's on the road for a few days. > You might want to wait for him. Hm, wait, Pat objected to the patch to kobject.c (now that I went back and read the whole thread.) And I agree with him, but I'm now getting an oops in get_kobj_path_length if I do the above while loading down the machine with other tasks when I cancel 'cat'. So something else bad is happening here... > > - kset_hotplug. It oopses in get_kobj_path_length because child->parent > > points to nowhere - even if parent has not yet been overwritten, its name > > is already freed. > > > > The patch moves kobject_put for parent from unlink() into > > kobject_cleanup for child making sure reference to parents exists for as > > long as child is there and may use it. But you can't do this, as you need that kobject_put() in unlink() for when it is called from kobject_add(). Hm, wait... I think we are close... Ok, here's how a parent can be removed from the system without the child going away: - create parent and register it successfully. - create child, call kobject_add() which increments the count of the parent. - call kobject_get() on the child. - call kobject_del() on the parent. This will keep the parent around, as the child still has a reference on it. - call kobject_del() on the child. This will decrement the count on the parent due to the call in unlink(). That will free the parent up from memory. But this child still has a incremented count (rightly, as it is in use). - So the child now has a stale parent pointer, causing all sorts of fun... I'll work on a patch for kobject.c and post it in the next message, and include the original message and patch below for others to see. thanks, greg k-h > > - after this oops has been fixed I got next one now in sysfs. The > > problem is sysfs_remove_dir would unlink all children including > > directories for subordinate kobjects. Resulting in dget/dput mismatch. > > I usually got oops due to the fact that d_delete in remove_dir would free > > inode and then simple_rmdir would try to access it. > > > > The patch avoids calling extra d_delete/unlink on already-deleted > > dentry. I hate this patch but anything better apparently requires > > complete redesign of sysfs implementation. Unlinking busy directory is > > otherwise impossible and I am afraid it will show itself somewhere else. > > > > > > > > 25-akpm/fs/sysfs/dir.c | 12 ++++++++++-- > > 25-akpm/lib/kobject.c | 4 ++-- > > 2 files changed, 12 insertions(+), 4 deletions(-) > > > > diff -puN fs/sysfs/dir.c~kobject-oops-fixes fs/sysfs/dir.c > > --- 25/fs/sysfs/dir.c~kobject-oops-fixes Thu Oct 9 01:46:51 2003 > > +++ 25-akpm/fs/sysfs/dir.c Thu Oct 9 01:46:51 2003 > > @@ -82,8 +82,16 @@ static void remove_dir(struct dentry * d > > { > > struct dentry * parent = dget(d->d_parent); > > down(&parent->d_inode->i_sem); > > - d_delete(d); > > - simple_rmdir(parent->d_inode,d); > > + /* > > + * It is possible that parent has already been removed, in which > > + * case directory is already unhashed and dput. > > + * Note that this won't update parent->d_inode->i_nlink; OTOH > > + * parent should already be dead > > + */ > > + if (!d_unhashed(d)) { > > + d_delete(d); > > + simple_rmdir(parent->d_inode,d); > > + } > > > > pr_debug(" o %s removing done (%d)\n",d->d_name.name, > > atomic_read(&d->d_count)); > > diff -puN lib/kobject.c~kobject-oops-fixes lib/kobject.c > > --- 25/lib/kobject.c~kobject-oops-fixes Thu Oct 9 01:46:51 2003 > > +++ 25-akpm/lib/kobject.c Thu Oct 9 01:46:51 2003 > > @@ -236,8 +236,6 @@ static void unlink(struct kobject * kobj > > list_del_init(&kobj->entry); > > up_write(&kobj->kset->subsys->rwsem); > > } > > - if (kobj->parent) > > - kobject_put(kobj->parent); > > kobject_put(kobj); > > } > > > > @@ -457,6 +455,8 @@ void kobject_cleanup(struct kobject * ko > > if (kobj->k_name != kobj->name) > > kfree(kobj->k_name); > > kobj->k_name = NULL; > > + if (kobj->parent) > > + kobject_put(kobj->parent); > > if (t && t->release) > > t->release(kobj); > > if (s) > > > > _ ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) 2003-12-08 22:48 ` oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) Greg KH @ 2003-12-08 22:58 ` Greg KH 2003-12-11 16:51 ` Patrick Mochel 2003-12-28 12:38 ` Andrey Borzenkov 1 sibling, 1 reply; 6+ messages in thread From: Greg KH @ 2003-12-08 22:58 UTC (permalink / raw) To: Andrew Morton, maneesh, mgorse, linux-kernel, Andrey Borzenkov, Patrick Mochel On Mon, Dec 08, 2003 at 02:48:10PM -0800, Greg KH wrote: > > Ok, here's how a parent can be removed from the system without the child > going away: > - create parent and register it successfully. > - create child, call kobject_add() which increments the count of > the parent. > - call kobject_get() on the child. > - call kobject_del() on the parent. This will keep the parent > around, as the child still has a reference on it. > - call kobject_del() on the child. This will decrement the > count on the parent due to the call in unlink(). That will > free the parent up from memory. But this child still has a > incremented count (rightly, as it is in use). > > - So the child now has a stale parent pointer, causing all sorts > of fun... > > I'll work on a patch for kobject.c and post it in the next message, and > include the original message and patch below for others to see. Here's a patch for kobject.c that should fix this problem and keep kobject parent's around until after the child is gone. Please can someone verify that I didn't get this wrong... thanks, greg k-h --- a/lib/kobject.c Mon Sep 29 15:13:44 2003 +++ b/lib/kobject.c Mon Dec 8 14:56:32 2003 @@ -236,8 +236,6 @@ list_del_init(&kobj->entry); up_write(&kobj->kset->subsys->rwsem); } - if (kobj->parent) - kobject_put(kobj->parent); kobject_put(kobj); } @@ -274,9 +272,11 @@ kobj->parent = parent; error = create_dir(kobj); - if (error) + if (error) { unlink(kobj); - else { + if (parent) + kobject_put(parent); + } else { /* If this kobj does not belong to a kset, try to find a parent that does. */ top_kobj = kobj; @@ -452,6 +452,7 @@ { struct kobj_type * t = get_ktype(kobj); struct kset * s = kobj->kset; + struct kobject * parent = kobj->parent; pr_debug("kobject %s: cleaning up\n",kobject_name(kobj)); if (kobj->k_name != kobj->name) @@ -461,6 +462,8 @@ t->release(kobj); if (s) kset_put(s); + if (parent) + kobject_put(parent); } /** ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) 2003-12-08 22:58 ` Greg KH @ 2003-12-11 16:51 ` Patrick Mochel 2003-12-11 17:50 ` Greg KH 0 siblings, 1 reply; 6+ messages in thread From: Patrick Mochel @ 2003-12-11 16:51 UTC (permalink / raw) To: Greg KH; +Cc: Andrew Morton, maneesh, mgorse, linux-kernel, Andrey Borzenkov Sorry about the delay in getting back to you. > Here's a patch for kobject.c that should fix this problem and keep > kobject parent's around until after the child is gone. Please can > someone verify that I didn't get this wrong... The patch looks good, please forward it on to Linus/Andrew. Thanks, Pat P.S. I've left OSDL to go work for a startup. Please use this email address from now on. ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) 2003-12-11 16:51 ` Patrick Mochel @ 2003-12-11 17:50 ` Greg KH 0 siblings, 0 replies; 6+ messages in thread From: Greg KH @ 2003-12-11 17:50 UTC (permalink / raw) To: Patrick Mochel Cc: Andrew Morton, maneesh, mgorse, linux-kernel, Andrey Borzenkov On Thu, Dec 11, 2003 at 08:51:58AM -0800, Patrick Mochel wrote: > > Sorry about the delay in getting back to you. > > > Here's a patch for kobject.c that should fix this problem and keep > > kobject parent's around until after the child is gone. Please can > > someone verify that I didn't get this wrong... > > The patch looks good, please forward it on to Linus/Andrew. Will do, thanks for looking it over. greg k-h ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) 2003-12-08 22:48 ` oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) Greg KH 2003-12-08 22:58 ` Greg KH @ 2003-12-28 12:38 ` Andrey Borzenkov 2003-12-30 0:32 ` Greg KH 1 sibling, 1 reply; 6+ messages in thread From: Andrey Borzenkov @ 2003-12-28 12:38 UTC (permalink / raw) To: Greg KH, Andrew Morton, maneesh, mgorse, linux-kernel; +Cc: Patrick Mochel On Tuesday 09 December 2003 01:48, Greg KH wrote: > Ok, I'm ccing lkml and everyone else who has been in on this thread at > different times. This is based on a patch from Andrey that was/is in > the -mm tree for a while. > what about second part in sysfs/dir.c? How relevant is it? -andrey > > > > - after this oops has been fixed I got next one now in sysfs. The > > > problem is sysfs_remove_dir would unlink all children including > > > directories for subordinate kobjects. Resulting in dget/dput > > > mismatch. I usually got oops due to the fact that d_delete in > > > remove_dir would free inode and then simple_rmdir would try to access > > > it. > > > > > > The patch avoids calling extra d_delete/unlink on already-deleted > > > dentry. I hate this patch but anything better apparently requires > > > complete redesign of sysfs implementation. Unlinking busy directory > > > is otherwise impossible and I am afraid it will show itself somewhere > > > else. > > > > > > > > > > > > 25-akpm/fs/sysfs/dir.c | 12 ++++++++++-- > > > 25-akpm/lib/kobject.c | 4 ++-- > > > 2 files changed, 12 insertions(+), 4 deletions(-) > > > > > > diff -puN fs/sysfs/dir.c~kobject-oops-fixes fs/sysfs/dir.c > > > --- 25/fs/sysfs/dir.c~kobject-oops-fixes Thu Oct 9 01:46:51 2003 > > > +++ 25-akpm/fs/sysfs/dir.c Thu Oct 9 01:46:51 2003 > > > @@ -82,8 +82,16 @@ static void remove_dir(struct dentry * d > > > { > > > struct dentry * parent = dget(d->d_parent); > > > down(&parent->d_inode->i_sem); > > > - d_delete(d); > > > - simple_rmdir(parent->d_inode,d); > > > + /* > > > + * It is possible that parent has already been removed, in which > > > + * case directory is already unhashed and dput. > > > + * Note that this won't update parent->d_inode->i_nlink; OTOH > > > + * parent should already be dead > > > + */ > > > + if (!d_unhashed(d)) { > > > + d_delete(d); > > > + simple_rmdir(parent->d_inode,d); > > > + } > > > > > > pr_debug(" o %s removing done (%d)\n",d->d_name.name, > > > atomic_read(&d->d_count)); ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) 2003-12-28 12:38 ` Andrey Borzenkov @ 2003-12-30 0:32 ` Greg KH 0 siblings, 0 replies; 6+ messages in thread From: Greg KH @ 2003-12-30 0:32 UTC (permalink / raw) To: Andrey Borzenkov Cc: Andrew Morton, maneesh, mgorse, linux-kernel, Patrick Mochel On Sun, Dec 28, 2003 at 03:38:42PM +0300, Andrey Borzenkov wrote: > On Tuesday 09 December 2003 01:48, Greg KH wrote: > > Ok, I'm ccing lkml and everyone else who has been in on this thread at > > different times. This is based on a patch from Andrey that was/is in > > the -mm tree for a while. > > > > what about second part in sysfs/dir.c? How relevant is it? Very relevant, that's why it's in the -mm tree right now :) thanks, greg k-h ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2003-12-30 0:34 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <20031009014837.4ff71634.akpm@osdl.org> [not found] ` <20031208222526.GA31134@kroah.com> 2003-12-08 22:48 ` oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) Greg KH 2003-12-08 22:58 ` Greg KH 2003-12-11 16:51 ` Patrick Mochel 2003-12-11 17:50 ` Greg KH 2003-12-28 12:38 ` Andrey Borzenkov 2003-12-30 0:32 ` Greg KH
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