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Mateusz Guzik a7031f1452 kernel/fork: stop playing lockless games for exe_file replacement 
xchg originated in 6e399cd144 ("prctl: avoid using mmap_sem for exe_file
serialization").  While the commit message does not explain *why* the
change, I found the original submission [1] which ultimately claims it
cleans things up by removing dependency of exe_file on the semaphore.

However, fe69d560b5 ("kernel/fork: always deny write access to current
MM exe_file") added a semaphore up/down cycle to synchronize the state of
exe_file against fork, defeating the point of the original change.

This is on top of semaphore trips already present both in the replacing
function and prctl (the only consumer).

Normally replacing exe_file does not happen for busy processes, thus
write-locking is not an impediment to performance in the intended use
case.  If someone keeps invoking the routine for a busy processes they are
trying to play dirty and that's another reason to avoid any trickery.

As such I think the atomic here only adds complexity for no benefit.

Just write-lock around the replacement.

I also note that replacement races against the mapping check loop as
nothing synchronizes actual assignment with with said checks but I am not
addressing it in this patch.  (Is the loop of any use to begin with?)

Link: https://lore.kernel.org/linux-mm/1424979417.10344.14.camel@stgolabs.net/ [1]
Link: https://lkml.kernel.org/r/20230814172140.1777161-1-mjguzik@gmail.com
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: "Christian Brauner (Microsoft)" <brauner@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-08-21 13:46:24 -07:00
..
9p fs/9p: Remove unused extern declaration 2023-07-20 19:21:48 +00:00
adfs adfs: delete unused "union adfs_dirtail" definition 2023-08-21 13:46:23 -07:00
affs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
afs afs: Fix accidental truncation when storing data 2023-07-04 12:24:32 -07:00
autofs arch/*/configs/*defconfig: Replace AUTOFS4_FS by AUTOFS_FS 2023-07-29 14:08:22 -07:00
befs befs: Replace all non-returning strlcpy with strscpy 2023-05-30 16:42:00 -07:00
bfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
btrfs for-6.5-rc3-tag 2023-07-27 11:44:08 -07:00
cachefiles v6.5/vfs.file 2023-06-26 10:14:36 -07:00
ceph ceph: never send metrics if disable_send_metrics is set 2023-07-24 13:15:39 +02:00
coda coda: Implement splice-read 2023-05-24 08:42:16 -06:00
configfs fs: consolidate duplicate dt_type helpers 2023-04-03 09:23:54 +02:00
cramfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
crypto fscrypt: Replace 1-element array with flexible array 2023-05-23 19:46:09 -07:00
debugfs debugfs: Correct the 'debugfs_create_str' docs 2023-05-31 19:02:14 +01:00
devpts devpts: simplify two-level sysctl registration for pty_kern_table 2023-03-13 12:36:34 +01:00
dlm dlm for 6.5 2023-06-29 13:27:50 -07:00
ecryptfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
efivarfs efivarfs: expose used and total size 2023-05-17 18:21:34 +02:00
efs efs: clean up -Wunused-const-variable= warning 2023-08-18 10:18:59 -07:00
erofs erofs: fix fsdax unavailability for chunk-based regular files 2023-07-12 00:50:56 +08:00
exfat splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
exportfs exportfs: add explicit flag to request non-decodeable file handles 2023-05-22 18:08:37 +02:00
ext2 \n 2023-06-29 13:39:51 -07:00
ext4 ext4: fix rbtree traversal bug in ext4_mb_use_preallocated 2023-07-23 08:21:14 -04:00
f2fs f2fs update for 6.5-rc1 2023-07-05 14:14:37 -07:00
fat splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
freevxfs There is no particular theme here - mainly quick hits all over the tree. 2023-02-23 17:55:40 -08:00
fscache fscache: Use clear_and_wake_up_bit() in fscache_create_volume_work() 2023-01-30 12:51:54 +00:00
fuse fuse update for 6.5 2023-07-19 11:00:27 -07:00
gfs2 gfs2 fixes 2023-07-04 11:45:16 -07:00
hfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
hfsplus fs: hfsplus: make extend error rate limited 2023-08-18 10:18:55 -07:00
hostfs Landlock updates for v6.5-rc1 2023-06-27 17:10:27 -07:00
hpfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
hugetlbfs hugetlb: revert use of page_cache_next_miss() 2023-06-23 16:59:32 -07:00
iomap iomap: micro optimize the ki_pos assignment in iomap_file_buffered_write 2023-07-17 08:49:57 -07:00
isofs
jbd2 jbd2: remove __journal_try_to_free_buffer() 2023-07-10 23:09:21 -04:00
jffs2 for-6.5/splice-2023-06-23 2023-06-26 11:52:12 -07:00
jfs Minor bug fixes and cleanups 2023-06-29 13:10:32 -07:00
kernfs driver core changes for 6.5-rc1 2023-07-03 12:56:23 -07:00
lockd NFS client updates for Linux 6.5 2023-07-01 14:38:25 -07:00
minix splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
netfs Move netfs_extract_iter_to_sg() to lib/scatterlist.c 2023-06-08 13:42:33 +02:00
nfs NFS client updates for Linux 6.5 2023-07-01 14:38:25 -07:00
nfs_common NFSv4.2: remove MODULE_LICENSE in non-modules 2023-04-13 13:13:52 -07:00
nfsd nfsd-6.5 fixes: 2023-07-25 13:54:04 -07:00
nilfs2 for-6.5/block-2023-06-23 2023-06-26 12:47:20 -07:00
nls fs/nls: make load_nls() take a const parameter 2023-07-25 00:30:02 -05:00
notify fanotify: disallow mount/sb marks on kernel internal pseudo fs 2023-07-04 13:29:29 +02:00
ntfs - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
ntfs3 driver ntfs3 for linux 6.5 2023-07-07 14:59:38 -07:00
ocfs2 fs: ocfs2: namei: check return value of ocfs2_add_entry() 2023-08-18 10:19:00 -07:00
omfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
openpromfs
orangefs orangefs: Provide a splice-read wrapper 2023-05-24 08:42:16 -06:00
overlayfs ovl: Always reevaluate the file signature for IMA 2023-07-25 15:36:22 -07:00
proc proc/vmcore: fix signedness bug in read_from_oldmem() 2023-07-27 13:07:05 -07:00
pstore pstore updates for v6.5-rc1 2023-06-27 21:21:32 -07:00
qnx4 qnx4: credit contributors in CREDITS 2023-03-14 12:56:30 -06:00
qnx6 qnx6: credit contributor and mark filesystem orphan 2023-03-14 12:56:30 -06:00
quota quota: fix warning in dqgrab() 2023-06-05 16:50:30 +02:00
ramfs - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
reiserfs - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
romfs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
smb four small client fixes 2023-07-29 20:49:13 -07:00
squashfs squashfs: fix cache race with migration 2023-07-08 09:29:30 -07:00
sysfs sysfs: Skip empty folders creation 2023-06-15 13:37:53 +02:00
sysv for-6.5/splice-2023-06-23 2023-06-26 11:52:12 -07:00
tracefs fs: port ->mkdir() to pass mnt_idmap 2023-01-19 09:24:26 +01:00
ubifs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
udf \n 2023-06-29 13:39:51 -07:00
ufs splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
unicode unicode: remove MODULE_LICENSE in non-modules 2023-04-13 13:13:54 -07:00
vboxsf hardening updates for v6.5-rc1 2023-06-27 21:24:18 -07:00
verity fsverity: improve documentation for builtin signature support 2023-06-20 22:47:55 -07:00
xfs xfs: convert flex-array declarations in xfs attr shortform objects 2023-07-17 08:48:56 -07:00
zonefs - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
aio.c fs/aio: Stop allocating aio rings from HIGHMEM 2023-06-15 09:22:23 +02:00
anon_inodes.c
attr.c nfs: use vfs setgid helper 2023-03-30 08:51:48 +02:00
bad_inode.c fs: port ->permission() to pass mnt_idmap 2023-01-19 09:24:28 +01:00
binfmt_elf_fdpic.c binfmt: Slightly simplify elf_fdpic_map_file() 2023-05-30 15:49:46 -07:00
binfmt_elf_test.c
binfmt_elf.c Merge branch 'expand-stack' 2023-06-28 20:35:21 -07:00
binfmt_flat.c
binfmt_misc.c binfmt_misc: fix shift-out-of-bounds in check_special_flags 2022-12-02 13:57:04 -08:00
binfmt_script.c
buffer.c \n 2023-06-29 13:39:51 -07:00
char_dev.c vfs: Replace all non-returning strlcpy with strscpy 2023-05-15 09:42:01 +02:00
compat_binfmt_elf.c
coredump.c v6.5/vfs.misc 2023-06-26 09:50:21 -07:00
d_path.c fs: d_path: include internal.h 2023-05-17 09:16:59 +02:00
dax.c dax: enable dax fault handler to report VM_FAULT_HWPOISON 2023-06-26 07:54:23 -06:00
dcache.c
direct-io.c - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
drop_caches.c
eventfd.c eventfd: show the EFD_SEMAPHORE flag in fdinfo 2023-06-15 09:22:23 +02:00
eventpoll.c v6.5/vfs.misc 2023-06-26 09:50:21 -07:00
exec.c kernel/fork: stop playing lockless games for exe_file replacement 2023-08-21 13:46:24 -07:00
fcntl.c fs.idmapped.v6.3 2023-02-20 11:53:11 -08:00
fhandle.c fsnotify: move fsnotify_open() hook into do_dentry_open() 2023-06-12 10:43:45 +02:00
file_table.c fs: move cleanup from init_file() into its callers 2023-07-02 13:15:49 +02:00
file.c file: always lock position for FMODE_ATOMIC_POS 2023-07-24 10:16:36 -07:00
filesystems.c
fs_context.c fs: avoid empty option when generating legacy mount string 2023-06-07 21:49:55 +02:00
fs_parser.c ext4: journal_path mount options should follow links 2022-12-01 10:46:54 -05:00
fs_pin.c
fs_struct.c
fs_types.c
fs-writeback.c writeback: move wb_over_bg_thresh() call outside lock section 2023-06-09 16:25:14 -07:00
fsopen.c
init.c fs: port ->permission() to pass mnt_idmap 2023-01-19 09:24:28 +01:00
inode.c fs: don't assume arguments are non-NULL 2023-07-04 10:21:11 +02:00
internal.h v6.5/vfs.file 2023-06-26 10:14:36 -07:00
ioctl.c fs: port inode_owner_or_capable() to mnt_idmap 2023-01-19 09:24:29 +01:00
Kconfig smb: move client and server files to common directory fs/smb 2023-05-24 16:29:21 -05:00
Kconfig.binfmt
kernel_read_file.c
libfs.c fs: factor out a direct_write_fallback helper 2023-06-09 16:25:53 -07:00
locks.c filelocks: use mount idmapping for setlease permission check 2023-03-09 22:36:12 +01:00
Makefile for-6.5/block-2023-06-23 2023-06-26 12:47:20 -07:00
mbcache.c ext4: fix deadlock due to mbcache entry corruption 2022-12-08 21:49:25 -05:00
mnt_idmapping.c fs: move mnt_idmap 2023-01-19 09:24:30 +01:00
mount.h
mpage.c mpage: use folios in bio end_io handler 2023-04-18 16:30:02 -07:00
namei.c fs: no need to check source 2023-07-04 10:20:29 +02:00
namespace.c v6.5/vfs.mount 2023-06-26 10:27:04 -07:00
nsfs.c kill the last remaining user of proc_ns_fget() 2023-04-20 22:55:35 -04:00
open.c \n 2023-06-29 13:31:44 -07:00
pipe.c pipe: check for IOCB_NOWAIT alongside O_NONBLOCK 2023-05-12 17:17:27 +02:00
pnode.c fs: allow to mount beneath top mount 2023-05-19 04:30:22 +02:00
pnode.h fs: allow to mount beneath top mount 2023-05-19 04:30:22 +02:00
posix_acl.c acl: don't depend on IOP_XATTR 2023-03-06 09:59:20 +01:00
proc_namespace.c tty, proc, kernfs, random: Use copy_splice_read() 2023-05-24 08:42:16 -06:00
read_write.c splice: Use filemap_splice_read() instead of generic_file_splice_read() 2023-05-24 08:42:17 -06:00
readdir.c readdir: Replace one-element arrays with flexible-array members 2023-06-21 09:06:59 +02:00
remap_range.c fs: use UB-safe check for signed addition overflow in remap_verify_area 2023-05-24 11:03:59 +02:00
select.c
seq_file.c use less confusing names for iov_iter direction initializers 2022-11-25 13:01:55 -05:00
signalfd.c
splice.c splice, net: Fix splice_to_socket() for O_NONBLOCK socket 2023-07-26 21:56:06 -07:00
stack.c
stat.c fs.idmapped.v6.3 2023-02-20 11:53:11 -08:00
statfs.c statfs: enforce statfs[64] structure initialization 2023-05-17 15:20:17 +02:00
super.c \n 2023-06-29 13:39:51 -07:00
sync.c
sysctls.c sysctl: Refactor base paths registrations 2023-05-23 21:43:26 -07:00
timerfd.c
userfaultfd.c Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-06-23 16:58:19 -07:00
utimes.c fs.idmapped.v6.3 2023-02-20 11:53:11 -08:00
xattr.c fs: don't call posix_acl_listxattr in generic_listxattr 2023-05-17 15:25:20 +02:00