On Fri, 2010-09-10 at 08:28 -0700, Joel Becker wrote: > On Wed, Sep 08, 2010 at 01:53:27PM -0700, Nicholas A. Bellinger wrote: > > On Wed, 2010-09-08 at 12:26 -0700, Joel Becker wrote: > > So after re-running this again, I was a bit off about where the OOOPs is > > actually occuring. So, the OOPs does not occur during in the simple > > example here with the first unlink(2): > > > > unlink sub_child/group1/src_0/src_link > > > > but rather after the second unlink(2) is called after the first for > > src_link occurs: > > > > unlink sub_child/group2/dst_0/dst_link > > > > So back to the OOPs with the current TCM code example, on v2.6.36-rc3 > > this actually triggers a SLUB warning "Object already free" from inside > > of TCM code. This is attributed to the releasing a specific LUN ACLs > > from the second unlink(2)'s struct config_item_operations->drop_link(), > > that the first unlink had already released. This is because the first > > unlink(2) will currently assume that the remaining LUN ACLs are safe to > > release because, it still assumes the disabled check_link call. > > The trivial solution is to refcount your ACLs. You get both > allow_link() calls, so you should be able to increment a counter there, > and then drop them when the last drop_link() call is made. That will > keep your consumer structures around until all links are exhausted. > Hi Joel, So I am a bit confused wrt to this last response.. The ->check_link() patch and it's use in the fabric independent code within target_core_fabric_configfs.c does exactly this for the 'MappedLUN' symlink case, eg: requires the consumer to do the allow_link() + drop_link() refcounting, and add the API check into fs/configfs/symlink.c:configfs_unlink() Is there another form of configfs consumer refcounting that you had in mind beyond using an atomic_t for this with ->check_link() here..? http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=drivers/target/target_core_fabric_configfs.c;hb=refs/heads/lio-4.0#l675 So beyond a configfs consumer solution, what do you think about checking for the sub_child/group2/dst_0/dst_link style of symlink in fs/configfs/symlink.c:configfs_symlink() in order to add some form of internal refcount when the symlink source is within the same consumer LKM, but outside of the parent struct config_group..? This would involve the conversion of fs/configfs/symlink.c: configfs_unlink() path to check for the existence of this internal refcount and returning -EPERM when any sub_child/group2/dst_0/dst_link exist when 'unlink sub_child/group1/src_0/src_link' is attempted. What do you think..? Thanks! --nab -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
