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Linus Torvalds ef0ba05538 poll: fix performance regression due to out-of-line __put_user() 
The kernel test robot reported a -5.8% performance regression on the
"poll2" test of will-it-scale, and bisected it to commit d55564cfc2
("x86: Make __put_user() generate an out-of-line call").

I didn't expect an out-of-line __put_user() to matter, because no normal
core code should use that non-checking legacy version of user access any
more.  But I had overlooked the very odd poll() usage, which does a
__put_user() to update the 'revents' values of the poll array.

Now, Al Viro correctly points out that instead of updating just the
'revents' field, it would be much simpler to just copy the _whole_
pollfd entry, and then we could just use "copy_to_user()" on the whole
array of entries, the same way we use "copy_from_user()" a few lines
earlier to get the original values.

But that is not what we've traditionally done, and I worry that threaded
applications might be concurrently modifying the other fields of the
pollfd array.  So while Al's suggestion is simpler - and perhaps worth
trying in the future - this instead keeps the "just update revents"
model.

To fix the performance regression, use the modern "unsafe_put_user()"
instead of __put_user(), with the proper "user_write_access_begin()"
guarding in place. This improves code generation enormously.

Link: https://lore.kernel.org/lkml/20210107134723.GA28532@xsang-OptiPlex-9020/
Reported-by: kernel test robot <oliver.sang@intel.com>
Tested-by: Oliver Sang <oliver.sang@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Laight <David.Laight@aculab.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2021-01-08 11:06:29 -08:00
..
9p 9p for 5.11-rc1 2020-12-21 10:28:02 -08:00
adfs Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-10-24 12:26:05 -07:00
affs Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-10-24 12:26:05 -07:00
afs afs: Fix directory entry size calculation 2021-01-04 12:25:19 +00:00
autofs file: Replace ksys_close with close_fd 2020-12-10 12:42:59 -06:00
befs [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
bfs bfs: don't use WARNING: string when it's just info. 2020-12-15 22:46:18 -08:00
btrfs for-5.11-rc2-tag 2021-01-06 11:19:08 -08:00
cachefiles cachefiles: Handle readpage error correctly 2020-10-26 10:42:54 -07:00
ceph ceph: reencode gid_list when reconnecting 2020-12-28 20:34:32 +01:00
cifs Add SMB 2 support for getting and setting SACLs 2020-12-18 23:32:04 -06:00
coda docs: filesystems: convert coda.txt to ReST 2020-05-05 09:22:21 -06:00
configfs configfs: fix kernel-doc markup issue 2020-11-14 10:22:45 +01:00
cramfs [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
crypto f2fs-for-5.11-rc1 2020-12-17 11:18:00 -08:00
debugfs debugfs: remove return value of debugfs_create_devm_seqfile() 2020-10-30 08:37:39 +01:00
devpts
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dlm fs: dlm: check on existing node address 2020-11-10 12:14:20 -06:00
ecryptfs mm, treewide: rename kzfree() to kfree_sensitive() 2020-08-07 11:33:22 -07:00
efivarfs efivarfs: revert "fix memory leak in efivarfs_create()" 2020-11-25 16:55:02 +01:00
efs [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
erofs erofs: avoid using generic_block_bmap 2020-12-10 11:07:40 +08:00
exfat exfat: Avoid allocating upcase table using kcalloc() 2020-12-22 12:31:17 +09:00
exportfs exportfs: Add a function to return the raw output from fh_to_dentry() 2020-12-09 09:39:38 -05:00
ext2 ext2: Fix fall-through warnings for Clang 2020-11-23 10:36:53 +01:00
ext4 Various bug fixes and cleanups for ext4; no new features this cycle. 2020-12-24 14:16:02 -08:00
f2fs f2fs-for-5.11-rc1 2020-12-17 11:18:00 -08:00
fat [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
freevxfs
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fscache Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-06-03 16:27:18 -07:00
fuse fuse: fix bad inode 2020-12-10 15:33:14 +01:00
gfs2 gfs2: in signal_our_withdraw wait for unfreeze of _this_ fs only 2020-12-03 17:04:41 +01:00
hfs fs: Replace zero-length array with flexible-array member 2020-10-29 17:22:59 -05:00
hfsplus fs: Replace zero-length array with flexible-array member 2020-10-29 17:22:59 -05:00
hostfs fix hostfs_open() use of ->f_path.dentry 2020-12-21 21:42:29 -05:00
hpfs [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
hugetlbfs hugetlbfs: prevent filesystem stacking of hugetlbfs 2020-08-12 10:57:56 -07:00
iomap mm: memcontrol: Use helpers to read page's memcg data 2020-12-02 18:28:05 -08:00
isofs fs: Replace zero-length array with flexible-array member 2020-10-29 17:22:59 -05:00
jbd2 jbd2: add a helper to find out number of fast commit blocks 2020-12-17 13:30:45 -05:00
jffs2 jffs2: Fix NULL pointer dereference in rp_size fs option parsing 2020-12-13 21:57:21 +01:00
jfs jfs: Fix array index bounds check in dbAdjTree 2020-11-13 16:03:07 -06:00
kernfs fs/kernfs: remove the double check of dentry->inode 2020-12-09 19:03:49 +01:00
lockd fs/lockd: convert comma to semicolon 2020-12-16 07:57:37 -05:00
minix [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
nfs NFS client updates for Linux 5.11 2020-12-17 12:15:03 -08:00
nfs_common nfs_common: need lock during iterate through the list 2020-12-09 09:38:34 -05:00
nfsd \n 2020-12-17 10:56:27 -08:00
nilfs2 fs/nilfs2: remove some unused macros to tame gcc 2020-12-15 22:46:17 -08:00
nls treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
notify \n 2020-12-17 10:56:27 -08:00
ntfs fs/ntfs: remove unused variable attr_len 2020-12-15 12:13:37 -08:00
ocfs2 ocfs2: ratelimit the 'max lookup times reached' notice 2020-12-15 12:13:37 -08:00
omfs fs: omfs: use kmemdup() rather than kmalloc+memcpy 2020-09-22 23:39:45 -04:00
openpromfs
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orangefs orangefs: add splice file operations 2020-12-16 16:14:08 -05:00
overlayfs ovl: unprivieged mounts 2020-12-14 15:26:14 +01:00
proc seccomp updates for v5.11-rc1 2020-12-16 11:30:10 -08:00
pstore Tracing updates for 5.11 2020-12-17 13:22:17 -08:00
qnx4 [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
qnx6 [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
quota \n 2020-12-17 11:00:37 -08:00
ramfs ramfs: fix nommu mmap with gaps in the page cache 2020-10-16 11:11:22 -07:00
reiserfs reiserfs: add check for an invalid ih_entry_count 2020-11-26 16:57:28 +01:00
romfs Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-10-24 12:26:05 -07:00
squashfs Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-10-24 12:26:05 -07:00
sysfs sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output 2020-10-02 12:02:30 +02:00
sysv [PATCH] reduce boilerplate in fsid handling 2020-09-18 16:45:50 -04:00
tracefs
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ubifs This pull request contains changes for JFFS2, UBI and UBIFS: 2020-12-17 17:46:34 -08:00
udf Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-10-24 12:26:05 -07:00
ufs Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-10-24 12:26:05 -07:00
unicode unicode: Add utf8_casefold_hash 2020-09-10 14:03:31 -07:00
vboxsf Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2020-10-15 15:11:56 -07:00
verity Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-12-14 12:18:19 -08:00
xfs New code for 5.11: 2020-12-18 12:50:18 -08:00
zonefs zonefs: fix page reference and BIO leak 2020-12-10 15:14:19 +09:00
Kconfig tmpfs: support 64-bit inums per-sb 2020-08-07 11:33:24 -07:00
Kconfig.binfmt treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
Makefile Refactored code for 5.10: 2020-10-23 11:33:41 -07:00
aio.c Merge branch 'akpm' (patches from Andrew) 2020-12-15 12:53:37 -08:00
anon_inodes.c
…
attr.c
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bad_inode.c fs: move the fiemap definitions out of fs.h 2020-06-03 23:16:55 -04:00
binfmt_aout.c exec: Rename flush_old_exec begin_new_exec 2020-05-07 16:55:47 -05:00
binfmt_elf.c Merge branch 'exec-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2020-12-15 19:29:43 -08:00
binfmt_elf_fdpic.c binfmt_elf, binfmt_elf_fdpic: use a VMA list snapshot 2020-10-16 11:11:21 -07:00
binfmt_em86.c Merge branch 'akpm' (patches from Andrew) 2020-06-04 19:18:29 -07:00
binfmt_flat.c binfmt_flat: revert "binfmt_flat: don't offset the data start" 2020-08-24 08:49:13 +10:00
binfmt_misc.c Merge branch 'akpm' (patches from Andrew) 2020-06-04 19:18:29 -07:00
binfmt_script.c Merge branch 'akpm' (patches from Andrew) 2020-06-04 19:18:29 -07:00
block_dev.c fs: block_dev.c: fix kernel-doc warnings from struct block_device changes 2020-12-29 16:47:18 -07:00
buffer.c for-5.11/block-2020-12-14 2020-12-16 12:57:51 -08:00
char_dev.c vfs: allow unprivileged whiteout creation 2020-05-14 16:44:23 +02:00
compat_binfmt_elf.c elf: Expose ELF header on arch_setup_additional_pages() 2020-10-26 13:46:47 +01:00
coredump.c Merge branch 'exec-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2020-12-15 19:29:43 -08:00
d_path.c fs: fix NULL dereference due to data race in prepend_path() 2020-10-14 14:54:45 -07:00
dax.c mm: simplify follow_pte{,pmd} 2020-12-15 22:46:19 -08:00
dcache.c fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set 2020-12-10 17:33:17 -05:00
dcookies.c
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direct-io.c \n 2020-10-15 15:03:10 -07:00
drop_caches.c sysctl: pass kernel pointers to ->proc_handler 2020-04-27 02:07:40 -04:00
eventfd.c eventfd: Export eventfd_ctx_do_read() 2020-11-15 09:49:10 -05:00
eventpoll.c epoll: add syscall epoll_pwait2 2020-12-19 11:18:38 -08:00
exec.c Merge branch 'parisc-5.11-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux 2020-12-16 12:10:40 -08:00
fcntl.c fcntl: Fix potential deadlock in send_sig{io, urg}() 2020-11-05 07:44:15 -05:00
fhandle.c
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file.c kernel/io_uring: cancel io_uring before task works 2020-12-30 19:36:54 -07:00
file_table.c epoll: take epitem list out of struct file 2020-10-25 20:02:08 -04:00
filesystems.c fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once() 2020-04-10 15:36:22 -07:00
fs-writeback.c writeback: don't warn on an unregistered BDI in __mark_inode_dirty 2020-12-16 11:56:02 +01:00
fs_context.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
fs_parser.c fs_parse: mark fs_param_bad_value() as static 2020-10-13 18:38:27 -07:00
fs_pin.c
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fs_struct.c vfs: Use sequence counter with associated spinlock 2020-07-29 16:14:27 +02:00
fs_types.c
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fsopen.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
init.c init: add an init_dup helper 2020-08-04 21:02:38 -04:00
inode.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-12-25 10:54:29 -08:00
internal.h for-5.11/block-2020-12-14 2020-12-16 12:57:51 -08:00
io-wq.c io-wq: kill now unused io_wq_cancel_all() 2020-12-20 10:47:42 -07:00
io-wq.h io-wq: kill now unused io_wq_cancel_all() 2020-12-20 10:47:42 -07:00
io_uring.c io_uring: fix io_sqe_files_unregister() hangs 2020-12-30 19:35:53 -07:00
ioctl.c fs: remove ksys_ioctl 2020-07-31 08:16:01 +02:00
kernel_read_file.c fs/kernel_file_read: Add "offset" arg for partial reads 2020-10-05 13:37:04 +02:00
libfs.c f2fs-for-5.11-rc1 2020-12-17 11:18:00 -08:00
locks.c Merge branch 'exec-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2020-12-15 19:29:43 -08:00
mbcache.c
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mount.h mnt: Use generic ns_common::count 2020-08-19 14:14:19 +02:00
mpage.c fs: convert mpage_readpages to mpage_readahead 2020-06-02 10:59:07 -07:00
namei.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-12-25 10:54:29 -08:00
namespace.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-12-25 10:54:29 -08:00
no-block.c
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nsfs.c nsproxy: attach to namespaces via pidfds 2020-05-13 11:41:22 +02:00
open.c Merge branch 'exec-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2020-12-15 19:29:43 -08:00
pipe.c block: remove i_bdev 2020-12-01 14:53:39 -07:00
pnode.c propagate_one(): mnt_set_mountpoint() needs mount_lock 2020-04-27 10:37:14 -04:00
pnode.h fs/namespace.c: WARN if mnt_count has become negative 2020-12-10 17:33:17 -05:00
posix_acl.c vfs: clean up posix_acl_permission() logic aroudn MAY_NOT_BLOCK 2020-06-08 11:04:19 -07:00
proc_namespace.c proc mountinfo: make splice available again 2020-12-27 12:00:36 -08:00
read_write.c Refactored code for 5.10: 2020-10-23 11:33:41 -07:00
readdir.c fs: remove ksys_getdents64 2020-07-31 08:16:00 +02:00
remap_range.c vfs: verify source area in vfs_dedupe_file_range_one() 2020-12-14 15:26:13 +01:00
select.c poll: fix performance regression due to out-of-line __put_user() 2021-01-08 11:06:29 -08:00
seq_file.c fix return values of seq_read_iter() 2020-11-15 22:12:53 -05:00
signalfd.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
splice.c io_uring-5.10-2020-10-24 2020-10-24 12:40:18 -07:00
stack.c
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stat.c fs: remove KSTAT_QUERY_FLAGS 2020-09-26 22:55:05 -04:00
statfs.c block: remove i_bdev 2020-12-01 14:53:39 -07:00
super.c block: remove i_bdev 2020-12-01 14:53:39 -07:00
sync.c overlayfs update for 5.8 2020-06-09 15:40:50 -07:00
timerfd.c
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userfaultfd.c userfaultfd: add user-mode only option to unprivileged_userfaultfd sysctl knob 2020-12-15 12:13:46 -08:00
utimes.c fs: expose utimes_common 2020-07-31 08:16:01 +02:00
xattr.c vfs: move cap_convert_nscap() call into vfs_setxattr() 2020-12-14 15:26:13 +01:00