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f29507ce66
When a cookie is allocated that causes fscache_object structs to be
allocated, those objects are initialised with the cookie pointer, but
aren't blessed with a ref on that cookie unless the attachment is
successfully completed in fscache_attach_object().
If attachment fails because the parent object was dying or there was a
collision, fscache_attach_object() returns without incrementing the cookie
counter - but upon failure of this function, the object is released which
then puts the cookie, whether or not a ref was taken on the cookie.
Fix this by taking a ref on the cookie when it is assigned in
fscache_object_init(), even when we're creating a root object.
Analysis from Kiran Kumar:
This bug has been seen in 4.4.0-124-generic #148-Ubuntu kernel
BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1776277
fscache cookie ref count updated incorrectly during fscache object
allocation resulting in following Oops.
kernel BUG at /build/linux-Y09MKI/linux-4.4.0/fs/fscache/internal.h:321!
kernel BUG at /build/linux-Y09MKI/linux-4.4.0/fs/fscache/cookie.c:639!
[Cause]
Two threads are trying to do operate on a cookie and two objects.
(1) One thread tries to unmount the filesystem and in process goes over a
huge list of objects marking them dead and deleting the objects.
cookie->usage is also decremented in following path:
nfs_fscache_release_super_cookie
-> __fscache_relinquish_cookie
->__fscache_cookie_put
->BUG_ON(atomic_read(&cookie->usage) <= 0);
(2) A second thread tries to lookup an object for reading data in following
path:
fscache_alloc_object
1) cachefiles_alloc_object
-> fscache_object_init
-> assign cookie, but usage not bumped.
2) fscache_attach_object -> fails in cant_attach_object because the
cookie's backing object or cookie's->parent object are going away
3) fscache_put_object
-> cachefiles_put_object
->fscache_object_destroy
->fscache_cookie_put
->BUG_ON(atomic_read(&cookie->usage) <= 0);
[NOTE from dhowells] It's unclear as to the circumstances in which (2) can
take place, given that thread (1) is in nfs_kill_super(), however a
conflicting NFS mount with slightly different parameters that creates a
different superblock would do it. A backtrace from Kiran seems to show
that this is a possibility:
kernel BUG at/build/linux-Y09MKI/linux-4.4.0/fs/fscache/cookie.c:639!
...
RIP: __fscache_cookie_put+0x3a/0x40 [fscache]
Call Trace:
__fscache_relinquish_cookie+0x87/0x120 [fscache]
nfs_fscache_release_super_cookie+0x2d/0xb0 [nfs]
nfs_kill_super+0x29/0x40 [nfs]
deactivate_locked_super+0x48/0x80
deactivate_super+0x5c/0x60
cleanup_mnt+0x3f/0x90
__cleanup_mnt+0x12/0x20
task_work_run+0x86/0xb0
exit_to_usermode_loop+0xc2/0xd0
syscall_return_slowpath+0x4e/0x60
int_ret_from_sys_call+0x25/0x9f
[Fix] Bump up the cookie usage in fscache_object_init, when it is first
being assigned a cookie atomically such that the cookie is added and bumped
up if its refcount is not zero. Remove the assignment in
fscache_attach_object().
[Testcase]
I have run ~100 hours of NFS stress tests and not seen this bug recur.
[Regression Potential]
- Limited to fscache/cachefiles.
Fixes:
|
||
|---|---|---|
| .. | ||
| 9p | ||
| adfs | ||
| affs | ||
| afs | ||
| autofs | ||
| befs | ||
| bfs | ||
| btrfs | ||
| cachefiles | ||
| ceph | ||
| cifs | ||
| coda | ||
| configfs | ||
| cramfs | ||
| crypto | ||
| debugfs | ||
| devpts | ||
| dlm | ||
| ecryptfs | ||
| efivarfs | ||
| efs | ||
| exofs | ||
| exportfs | ||
| ext2 | ||
| ext4 | ||
| f2fs | ||
| fat | ||
| freevxfs | ||
| fscache | ||
| fuse | ||
| gfs2 | ||
| hfs | ||
| hfsplus | ||
| hostfs | ||
| hpfs | ||
| hugetlbfs | ||
| isofs | ||
| jbd2 | ||
| jffs2 | ||
| jfs | ||
| kernfs | ||
| lockd | ||
| minix | ||
| nfs | ||
| nfs_common | ||
| nfsd | ||
| nilfs2 | ||
| nls | ||
| notify | ||
| ntfs | ||
| ocfs2 | ||
| omfs | ||
| openpromfs | ||
| orangefs | ||
| overlayfs | ||
| proc | ||
| pstore | ||
| qnx4 | ||
| qnx6 | ||
| quota | ||
| ramfs | ||
| reiserfs | ||
| romfs | ||
| squashfs | ||
| sysfs | ||
| sysv | ||
| tracefs | ||
| ubifs | ||
| udf | ||
| ufs | ||
| xfs | ||
| aio.c | ||
| anon_inodes.c | ||
| attr.c | ||
| bad_inode.c | ||
| binfmt_aout.c | ||
| binfmt_elf_fdpic.c | ||
| binfmt_elf.c | ||
| binfmt_em86.c | ||
| binfmt_flat.c | ||
| binfmt_misc.c | ||
| binfmt_script.c | ||
| block_dev.c | ||
| buffer.c | ||
| char_dev.c | ||
| compat_binfmt_elf.c | ||
| compat_ioctl.c | ||
| compat.c | ||
| coredump.c | ||
| d_path.c | ||
| dax.c | ||
| dcache.c | ||
| dcookies.c | ||
| direct-io.c | ||
| drop_caches.c | ||
| eventfd.c | ||
| eventpoll.c | ||
| exec.c | ||
| fcntl.c | ||
| fhandle.c | ||
| file_table.c | ||
| file.c | ||
| filesystems.c | ||
| fs_pin.c | ||
| fs_struct.c | ||
| fs-writeback.c | ||
| inode.c | ||
| internal.h | ||
| ioctl.c | ||
| iomap.c | ||
| Kconfig | ||
| Kconfig.binfmt | ||
| libfs.c | ||
| locks.c | ||
| Makefile | ||
| mbcache.c | ||
| mount.h | ||
| mpage.c | ||
| namei.c | ||
| namespace.c | ||
| no-block.c | ||
| nsfs.c | ||
| open.c | ||
| pipe.c | ||
| pnode.c | ||
| pnode.h | ||
| posix_acl.c | ||
| proc_namespace.c | ||
| read_write.c | ||
| readdir.c | ||
| select.c | ||
| seq_file.c | ||
| signalfd.c | ||
| splice.c | ||
| stack.c | ||
| stat.c | ||
| statfs.c | ||
| super.c | ||
| sync.c | ||
| timerfd.c | ||
| userfaultfd.c | ||
| utimes.c | ||
| xattr.c | ||