b61f7dcf4e
The afs directory loading code (primarily afs_read_dir()) locks all the
pages that hold a directory's content blob to defend against
getdents/getdents races and getdents/lookup races where the competitors
issue conflicting reads on the same data. As the reads will complete
consecutively, they may retrieve different versions of the data and
one may overwrite the data that the other is busy parsing.
Fix this by not locking the pages at all, but rather by turning the
validation lock into an rwsem and getting an exclusive lock on it whilst
reading the data or validating the attributes and a shared lock whilst
parsing the data. Sharing the attribute validation lock should be fine as
the data fetch will retrieve the attributes also.
The individual page locks aren't needed at all as the only place they're
being used is to serialise data loading.
Without this patch, the:
if (!test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags)) {
...
}
part of afs_read_dir() may be skipped, leaving the pages unlocked when we
hit the success: clause - in which case we try to unlock the not-locked
pages, leading to the following oops:
page:ffffe38b405b4300 count:3 mapcount:0 mapping:ffff98156c83a978 index:0x0
flags: 0xfffe000001004(referenced|private)
raw: 000fffe000001004 ffff98156c83a978 0000000000000000 00000003ffffffff
raw: dead000000000100 dead000000000200 0000000000000001 ffff98156b27c000
page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
page->mem_cgroup:ffff98156b27c000
------------[ cut here ]------------
kernel BUG at mm/filemap.c:1205!
...
RIP: 0010:unlock_page+0x43/0x50
...
Call Trace:
afs_dir_iterate+0x789/0x8f0 [kafs]
? _cond_resched+0x15/0x30
? kmem_cache_alloc_trace+0x166/0x1d0
? afs_do_lookup+0x69/0x490 [kafs]
? afs_do_lookup+0x101/0x490 [kafs]
? key_default_cmp+0x20/0x20
? request_key+0x3c/0x80
? afs_lookup+0xf1/0x340 [kafs]
? __lookup_slow+0x97/0x150
? lookup_slow+0x35/0x50
? walk_component+0x1bf/0x490
? path_lookupat.isra.52+0x75/0x200
? filename_lookup.part.66+0xa0/0x170
? afs_end_vnode_operation+0x41/0x60 [kafs]
? __check_object_size+0x9c/0x171
? strncpy_from_user+0x4a/0x170
? vfs_statx+0x73/0xe0
? __do_sys_newlstat+0x39/0x70
? __x64_sys_getdents+0xc9/0x140
? __x64_sys_getdents+0x140/0x140
? do_syscall_64+0x5b/0x160
? entry_SYSCALL_64_after_hwframe+0x44/0xa9
Fixes:
|
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.