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f47d223627
Please consider pulling these changes from the signed vfs-7.4-rc1.sync_close tag.
Thanks!
Christian
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Merge tag 'vfs-7.4-rc1.sync_close' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull file closing updates from Christian Brauner:
"This makes closing files synchronous for close_range(), exec and exit.
Since fput() was switched to task work every final __fput() of an
exiting task is queued on task work and run from exit_task_work().
exec and close_range() do the same. For a task with a large descriptor
table that is a cmpxchg() and a TIF_NOTIFY_RESUME test-and-set per
file plus a list entry for any later task_work_cancel() to search
under pi_lock, and then a second pass over every struct file that
isn't cache hot anymore by then. Oleg and Neil have pointed this out
over the years.
close_files(), close_range() and close-on-exec now flush and put each
file inline the way close(2) does. Kernel threads aren't affected.
They share init_files which init_task pins forever so their
exit_files() never drops the last reference, and their fput() keeps
punting to a workqueue. The one place that could put a table from a
kthread context, a failing copy_process(), can't hold the last
reference while the source table is alive.
On a 64 vCPU KVM guest tearing down 4096, 65536 and 1M descriptors
scattered at random positions in the table:
4096 fds 65536 fds 1M fds
exit 1045 -> 895 us 18.9 -> 14.9 ms 429 -> 306 ms
execve, close-on-exec 1393 -> 1190 us 21.4 -> 16.9 ms 471 -> 325 ms
close_range() 1179 -> 988 us 21.9 -> 17.4 ms 484 -> 337 ms
So that is 16-21% or 40-150 ns per closed file, largest at 1M
descriptors. With eight processes tearing down 65536 descriptors each
at once it stays at 16-21% because the second pass over 16 MB of
struct file is what gets expensive when CPUs compete for the cache.
With 32 or 64 processes both kernels are bound by pushing millions of
files through slab and rcu and the difference shrinks to 4-8%. Files
whose own release dominates gain less, 13% for eventfds, 11% for
pipes, 6% for AF_UNIX sockets. close(2) is untouched and will-it-scale
is within 2%.
The spufs coredump support is removed. It was the only reason
do_coredump() unshared the descriptor table. gdb dropped Cell
debugging in 9.1 and binutils in 2.34, the Cell blades are gone and
nothing on the PlayStation 3 produces or reads these notes. With that
unshare_files() goes away, exec installs its private table through the
new switch_files_struct() and the coredump startup completion becomes
a plain thread count waited on with the new wait_var_event_state().
Three fixes for the synchronous close are included. A failed fork
released its files under scx_fork_rwsem and deadlocked against the bpf
link's release. A session leader's exit released its tty before
disassociate_ctty() ran and the foreground job lost its SIGHUP, so the
tty is hung up before the files are closed now. And descriptor tables
are walked from the highest descriptor down which restores the order
the deferred puts had and keeps a few long-standing release ordering
bugs from deadlocking exit"
* tag 'vfs-7.4-rc1.sync_close' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
fs: close files from the highest descriptor down
coredump: factor out coredump_wait_inactive()
exit: hang up the tty before closing the files
fork: release the files of a failed fork after sched_cancel_fork()
coredump: replace the startup completion with a thread count
sched: add wait_var_event_state()
coredump: drop core_state->dumper
fs: make close_cloexec_files() synchronous
fs: rename do_close_on_exec() to close_cloexec_files()
fs: make close_range() synchronous
fs: make close_files() synchronous
fs: add filp_close_sync()
fs: remove unshare_files()
fs: move unshare_fd() to fs/file.c
fs: add switch_files_struct()
coredump: stop unsharing the file descriptor table
fs: don't open-code file_close_fd() in close_fd()
powerpc: remove coredump support
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