Messages in this thread | | | Subject | Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted inodes/dentries | From | "Steven J. Magnani" <> | Date | Sat, 07 Jul 2012 11:41:26 -0500 |
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On Sat, 2012-07-07 at 15:03 +0900, OGAWA Hirofumi wrote: > "Steven J. Magnani" <steve@digidescorp.com> writes: > > > On Sat, 2012-07-07 at 06:07 +0900, OGAWA Hirofumi wrote: > >> "Steven J. Magnani" <steve@digidescorp.com> writes: > >> > >> > On Wed, 2012-07-04 at 20:07 +0900, OGAWA Hirofumi wrote: > >> >> Please don't add new lock_super() usage if it is not necessary. Almost > >> >> all of lock_super() just replaced lock_kernel() usage. It rather should > >> >> be removed in future. Probably, this should use inode->i_mutex instead. > >> >> > >> >> BTW, the above issue is same with all of directory read. > >> > > >> > I don't think there's really an alternative here. The cases addressed by > >> > this patch all involve walking on-disk structures via > >> > unofficial/temporary inodes created from information in the NFS handle > >> > (i.e., outside the normal inode creation paths). When this process is > >> > successful we end up with "official" connected inodes/dentries, but > >> > getting there is really a "bottom up" strategy instead of the usual "top > >> > down" approach. > >> > > >> > Because the "bottom up" method is lacking guarantees that "top down" > >> > takes for granted - i.e., that a cluster on disk that's supposed to be a > >> > directory actually *is* a directory - I am adding some defensive code > >> > in the next spin of the patch. > >> > >> I'm not sure what you meant. Where is the problem? ->get_name()? If so, > >> it has parent dentry parameter. What is the wrong if we take > >> mutex_lock(parent->d_inode)? > > > > The temporary/"unofficial" inodes are unhashed and thus not visible > > outside of the functions using them. They exist only to support access > > to directory contents when we can't gain that access via other means > > (because we only have "bottom up" information, about an object and > > perhaps its parent, in a form that can't be used to look up hashed > > inodes/dentries). Hashing them wouldn't help, because they don't have > > the correct key (for instance, in the case of a ".." entry). > > > > Am I missing something? > > You mean the unhashed inode is created by ->get_parent()? If so, the > root cause sounds like ->get_parent() itself. If not, I'm not > understanding the meaning of the temporary/unofficial inode here.
Maybe "private" is a better word than "unofficial". Private inodes are created anywhere fat_new_inode (nee fat_build_unhashed_inode) is called directly, instead of through fat_build_inode. So yes, this is on the get_parent paths (via fat_lookup_dir), and also on the fh_to_dentry path when inode reconstruction is necessary.
With private inodes, I don't see how anyone but the code that created them could find them to lock them. The reason they're private is that they're temporary aliases; at the time they're created, we don't have enough information to register them in a way that others could find them. A lookup, etc. operation will look for the inode of the "drivers" directory, not the ".." of the "usb" directory. We do need these private inodes in order to walk directory entries. I don't think they're a problem that needs solving; if we didn't use private inodes, we'd still need a way to walk directory entries in the context of these NFS operations, and there would still be potential races between that and other operations on the filesystem.
------------------------------------------------------------------------ Steven J. Magnani "I claim this network for MARS! www.digidescorp.com Earthling, return my space modulator!"
#include <standard.disclaimer>
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