linux.git/fs/eventfd.c, branch v4.12

sched/headers: Prepare to move signal wakeup & sigpending methods from into

2017-03-02T07:42:32+00:00

Fix up affected files that include this signal functionality via sched.h.

Acked-by: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

eventfd: document lockless access in eventfd_poll

2016-03-22T22:36:02+00:00

Since commit e22553e2a25e ("eventfd: don't take the spinlock in
eventfd_poll", 2015-02-17), eventfd is reading ctx->count outside
ctx->wqh.lock.

However, things aren't as simple as the read barrier in eventfd_poll
would suggest.  In fact, the read barrier, besides lacking a comment, is
not paired in any obvious manner with another read barrier, and it is
pointless because it is sitting between a write (deep in poll_wait) and
the read of ctx->count.  The read barrier is acting just as a compiler
barrier, for which we can use READ_ONCE instead.  This is what the code
change in this patch does.

The documentation change is just as important, however.  The question,
posed by Andrea Arcangeli, is then why the thing is safe on
architectures where spin_unlock does not imply a store-load memory
barrier.  The answer is that it's safe because writes of ctx->count use
the same lock as poll_wait, and hence an acquire barrier implicit in
poll_wait provides the necessary synchronization between eventfd_poll
and callers of wake_up_locked_poll.  This is sort of mentioned in the
commit message with respect to eventfd_ctx_read ("eventfd_read is
similar, it will do a single decrement with the lock held") but it
applies to all other callers too.  It's tricky enough that it should be
documented in the code.

Signed-off-by: Paolo Bonzini 
Reviewed-by: Andrea Arcangeli 
Cc: Chris Mason 
Cc: Davide Libenzi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Documentation: filesystem: Fix typo in fs/eventfd.c

2015-12-08T13:52:03+00:00

This patch fix typos found in Documentation/filesystems.xml,
DocBook/filesystems/API-eventfd-signal.html, and
DocBook/filesystems.aux.xml

These files are generated from comments within the source,
so I had to fix typos in fs/eventfd.c

Signed-off-by: Masanari Iida 
Signed-off-by: Jiri Kosina

eventfd: don't take the spinlock in eventfd_poll

2015-02-17T22:34:52+00:00

The spinlock in eventfd_poll is trying to protect the count of events so
it can decide if it should return POLLIN, POLLERR, or POLLOUT.  But,
because of the way we drop the lock after calling poll_wait, and drop it
again before returning, we have the same pile of races with the lock as
we do with a single read of ctx->count().

This replaces the lock with a read barrier and single read.

eventfd_write does a single bump of ctx->count, so this should not add
new races with adding events.  eventfd_read is similar, it will do a
single decrement with the lock held, and so we're making the race with
concurrent readers slightly larger.

This spinlock is the top CPU user in kernel code during one of our
workloads.  Removing it gives us a ~2% boost.

[arnd@arndb.de: avoid unused variable warning]
[dan.carpenter@oracle.com: type bug in eventfd_poll()]
Signed-off-by: Chris Mason 
Cc: Davide Libenzi 
Signed-off-by: Arnd Bergmann 
Signed-off-by: Dan Carpenter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: Convert show_fdinfo functions to void

2014-11-05T19:13:23+00:00

seq_printf functions shouldn't really check the return value.
Checking seq_has_overflowed() occasionally is used instead.

Update vfs documentation.

Link: http://lkml.kernel.org/p/e37e6e7b76acbdcc3bb4ab2a57c8f8ca1ae11b9a.1412031505.git.joe@perches.com

Cc: David S. Miller 
Cc: Al Viro 
Signed-off-by: Joe Perches 
[ did a few clean ups ]
Signed-off-by: Steven Rostedt

eventfd_ctx_fdget(): use fdget() instead of fget()

2014-01-25T08:13:04+00:00

Signed-off-by: Al Viro

fs, eventfd: add procfs fdinfo helper

2012-12-18T01:15:27+00:00

This allows us to print out raw counter value.  The /proc/pid/fdinfo/fd
output is

 | pos:	0
 | flags:	04002
 | eventfd-count:               5a

Signed-off-by: Cyrill Gorcunov 
Acked-by: Pavel Emelyanov 
Cc: Oleg Nesterov 
Cc: Andrey Vagin 
Cc: Al Viro 
Cc: Alexey Dobriyan 
Cc: James Bottomley 
Cc: "Aneesh Kumar K.V" 
Cc: Alexey Dobriyan 
Cc: Matthew Helsley 
Cc: "J. Bruce Fields" 
Cc: "Aneesh Kumar K.V" 
Cc: Tvrtko Ursulin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

eventfd: change int to __u64 in eventfd_signal()

2012-06-01T00:49:32+00:00

eventfd_ctx->count is an __u64 counter which is allowed to reach
ULLONG_MAX.  eventfd_write() adds a __u64 value to "count", but the kernel
side eventfd_signal() only adds an int value to it.  Make them consistent.

[akpm@linux-foundation.org: update interface documentation]
Signed-off-by: Sha Zhengju 
Cc: Davide Libenzi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs: reduce the use of module.h wherever possible

2012-02-29T00:31:58+00:00

For files only using THIS_MODULE and/or EXPORT_SYMBOL, map
them onto including export.h -- or if the file isn't even
using those, then just delete the include.  Fix up any implicit
include dependencies that were being masked by module.h along
the way.

Signed-off-by: Paul Gortmaker

Docbook: add fs/eventfd.c and fix typos in it

2011-02-21T23:07:04+00:00

Add fs/eventfd.c to filesystems docbook.
Make typo corrections in fs/eventfd.c.

Signed-off-by: Randy Dunlap 
Cc: Davide Libenzi 
Signed-off-by: Linus Torvalds