linux.git/fs/eventpoll.c, branch v5.14

fs/epoll: restore waking from ep_done_scan()

2021-05-07T02:24:13+00:00

Commit 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested
epoll") changed the userspace visible behavior of exclusive waiters
blocked on a common epoll descriptor upon a single event becoming ready.

Previously, all tasks doing epoll_wait would awake, and now only one is
awoken, potentially causing missed wakeups on applications that rely on
this behavior, such as Apache Qpid.

While the aforementioned commit aims at having only a wakeup single path
in ep_poll_callback (with the exceptions of epoll_ctl cases), we need to
restore the wakeup in what was the old ep_scan_ready_list() such that
the next thread can be awoken, in a cascading style, after the waker's
corresponding ep_send_events().

Link: https://lkml.kernel.org/r/20210405231025.33829-3-dave@stgolabs.net
Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll")
Signed-off-by: Davidlohr Bueso 
Cc: Al Viro 
Cc: Jason Baron 
Cc: Roman Penyaev 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: eventpoll: fix comments & kernel-doc notation

2021-03-07T00:36:53+00:00

Use the documented kernel-doc format for function Return: descriptions.
Begin constant values in kernel-doc comments with '%'.

Remove kernel-doc "/**" from 2 functions that are not documented with
kernel-doc notation.

Fix typos, punctuation, & grammar.

Also fix a few kernel-doc warnings:

../fs/eventpoll.c:1883: warning: Function parameter or member 'ep' not described in 'ep_loop_check_proc'
../fs/eventpoll.c:1883: warning: Excess function parameter 'priv' description in 'ep_loop_check_proc'
../fs/eventpoll.c:1932: warning: Function parameter or member 'ep' not described in 'ep_loop_check'
../fs/eventpoll.c:1932: warning: Excess function parameter 'from' description in 'ep_loop_check'

Signed-off-by: Randy Dunlap 
Cc: Andrew Morton 
Cc: Alexander Viro 
Signed-off-by: Jonathan Corbet

kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE

2021-02-16T08:59:41+00:00

Userspace has discovered the functionality offered by SYS_kcmp and has
started to depend upon it. In particular, Mesa uses SYS_kcmp for
os_same_file_description() in order to identify when two fd (e.g. device
or dmabuf) point to the same struct file. Since they depend on it for
core functionality, lift SYS_kcmp out of the non-default
CONFIG_CHECKPOINT_RESTORE into the selectable syscall category.

Rasmus Villemoes also pointed out that systemd uses SYS_kcmp to
deduplicate the per-service file descriptor store.

Note that some distributions such as Ubuntu are already enabling
CHECKPOINT_RESTORE in their configs and so, by extension, SYS_kcmp.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/3046
Signed-off-by: Chris Wilson 
Cc: Kees Cook 
Cc: Andy Lutomirski 
Cc: Will Drewry 
Cc: Andrew Morton 
Cc: Dave Airlie 
Cc: Daniel Vetter 
Cc: Lucas Stach 
Cc: Rasmus Villemoes 
Cc: Cyrill Gorcunov 
Cc: stable@vger.kernel.org
Acked-by: Daniel Vetter  # DRM depends on kcmp
Acked-by: Rasmus Villemoes  # systemd uses kcmp
Reviewed-by: Cyrill Gorcunov 
Reviewed-by: Kees Cook 
Acked-by: Thomas Zimmermann 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20210205220012.1983-1-chris@chris-wilson.co.uk

epoll: add syscall epoll_pwait2

2020-12-19T19:18:38+00:00

Add syscall epoll_pwait2, an epoll_wait variant with nsec resolution that
replaces int timeout with struct timespec.  It is equivalent otherwise.

    int epoll_pwait2(int fd, struct epoll_event *events,
                     int maxevents,
                     const struct timespec *timeout,
                     const sigset_t *sigset);

The underlying hrtimer is already programmed with nsec resolution.
pselect and ppoll also set nsec resolution timeout with timespec.

The sigset_t in epoll_pwait has a compat variant. epoll_pwait2 needs
the same.

For timespec, only support this new interface on 2038 aware platforms
that define __kernel_timespec_t. So no CONFIG_COMPAT_32BIT_TIME.

Link: https://lkml.kernel.org/r/20201121144401.3727659-3-willemdebruijn.kernel@gmail.com
Signed-off-by: Willem de Bruijn 
Cc: Al Viro 
Cc: Arnd Bergmann 
Cc: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

epoll: convert internal api to timespec64

2020-12-19T19:18:38+00:00

Patch series "add epoll_pwait2 syscall", v4.

Enable nanosecond timeouts for epoll.

Analogous to pselect and ppoll, introduce an epoll_wait syscall
variant that takes a struct timespec instead of int timeout.

This patch (of 4):

Make epoll more consistent with select/poll: pass along the timeout as
timespec64 pointer.

In anticipation of additional changes affecting all three polling
mechanisms:

- add epoll_pwait2 syscall with timespec semantics,
  and share poll_select_set_timeout implementation.
- compute slack before conversion to absolute time,
  to save one ktime_get_ts64 call.

Link: https://lkml.kernel.org/r/20201121144401.3727659-1-willemdebruijn.kernel@gmail.com
Link: https://lkml.kernel.org/r/20201121144401.3727659-2-willemdebruijn.kernel@gmail.com
Signed-off-by: Willem de Bruijn 
Cc: Al Viro 
Cc: Matthew Wilcox (Oracle) 
Cc: Arnd Bergmann 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

epoll: eliminate unnecessary lock for zero timeout

2020-12-19T19:18:38+00:00

We call ep_events_available() under lock when timeout is 0, and then call
it without locks in the loop for the other cases.

Instead, call ep_events_available() without lock for all cases.  For
non-zero timeouts, we will recheck after adding the thread to the wait
queue.  For zero timeout cases, by definition, user is opportunistically
polling and will have to call epoll_wait again in the future.

Note that this lock was kept in c5a282e9635e9 because the whole loop was
historically under lock.

This patch results in a 1% CPU/RPC reduction in RPC benchmarks.

Link: https://lkml.kernel.org/r/20201106231635.3528496-9-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh 
Suggested-by: Eric Dumazet 
Reviewed-by: Eric Dumazet 
Reviewed-by: Willem de Bruijn 
Reviewed-by: Khazhismel Kumykov 
Cc: Guantao Liu 
Cc: Linus Torvalds 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

epoll: replace gotos with a proper loop

2020-12-19T19:18:38+00:00

The existing loop is pointless, and the labels make it really hard to
follow the structure.

Replace that control structure with a simple loop that returns when there
are new events, there is a signal, or the thread has timed out.

Link: https://lkml.kernel.org/r/20201106231635.3528496-8-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh 
Suggested-by: Linus Torvalds 
Reviewed-by: Eric Dumazet 
Reviewed-by: Willem de Bruijn 
Reviewed-by: Khazhismel Kumykov 
Cc: Guantao Liu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

epoll: pull all code between fetch_events and send_event into the loop

2020-12-19T19:18:38+00:00

This is a no-op change which simplifies the follow up patches.

Link: https://lkml.kernel.org/r/20201106231635.3528496-7-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh 
Suggested-by: Linus Torvalds 
Reviewed-by: Eric Dumazet 
Reviewed-by: Willem de Bruijn 
Reviewed-by: Khazhismel Kumykov 
Cc: Guantao Liu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

epoll: simplify and optimize busy loop logic

2020-12-19T19:18:37+00:00

ep_events_available() is called multiple times around the busy loop logic,
even though the logic is generally not used.  ep_reset_busy_poll_napi_id()
is similarly always called, even when busy loop is not used.

Eliminate ep_reset_busy_poll_napi_id() and inline it inside
ep_busy_loop().  Make ep_busy_loop() return whether there are any events
available after the busy loop.  This will eliminate unnecessary loads and
branches, and simplifies the loop.

Link: https://lkml.kernel.org/r/20201106231635.3528496-6-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh 
Reviewed-by: Eric Dumazet 
Reviewed-by: Willem de Bruijn 
Reviewed-by: Khazhismel Kumykov 
Cc: Guantao Liu 
Cc: Linus Torvalds 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

epoll: move eavail next to the list_empty_careful check

2020-12-19T19:18:37+00:00

This is a no-op change and simply to make the code more coherent.

Link: https://lkml.kernel.org/r/20201106231635.3528496-5-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh 
Suggested-by: Linus Torvalds 
Reviewed-by: Eric Dumazet 
Reviewed-by: Willem de Bruijn 
Reviewed-by: Khazhismel Kumykov 
Cc: Guantao Liu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds