The powerpc user access code is special, and unlike other architectures
distinguishes between user access for reading and writing.
And commit 43a43faf53 ("futex: improve user space accesses") messed
that up. It went undetected elsewhere, but caused ppc32 to fail early
during boot, because the user access had been started with
user_read_access_begin(), but then finished off with just a plain
"user_access_end()".
Note that the address-masking user access helpers don't even have that
read-vs-write distinction, so if powerpc ever wants to do address
masking tricks, we'll have to do some extra work for it.
[ Make sure to also do it for the EFAULT case, as pointed out by
Christophe Leroy ]
Reported-by: Andreas Schwab <schwab@linux-m68k.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/all/87bjxl6b0i.fsf@igel.home/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Josh Poimboeuf reports that he got a "will-it-scale.per_process_ops 1.9%
improvement" report for his patch that changed __get_user() to use
pointer masking instead of the explicit speculation barrier. However,
that patch doesn't actually work in the general case, because some (very
bad) architecture-specific code actually depends on __get_user() also
working on kernel addresses.
A profile showed that the offending __get_user() was the futex code,
which really should be fixed up to not use that horrid legacy case.
Rewrite futex_get_value_locked() to use the modern user acccess helpers,
and inline it so that the compiler not only avoids the function call for
a few instructions, but can do CSE on the address masking.
It also turns out the x86 futex functions have unnecessary barriers in
other places, so let's fix those up too.
Link: https://lore.kernel.org/all/20241115230653.hfvzyf3aqqntgp63@jpoimboe/
Reported-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rename unqueue_multiple() as futex_unqueue_multiple(), and make both
that and futex_wait_multiple_setup() available for external users. This
is in preparation for wiring up vectored waits in io_uring.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
To make it more generically useful, augment it with allowing the caller
to pass in the wake handler and wake data. Convert the futex_waitv()
syscall, passing in the default handlers.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
With handling multiple futex_q for waitv, we cannot easily go from the
futex_q to data related to that request or queue. Add a wake_data
argument that belongs to the wake handler assigned.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Move the unqueue and lock_ptr clear into a helper that futex_wake_mark()
calls. Add it to the public functions as well, in preparation for using
it outside the core futex code.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In preparation for having another waker that isn't futex_wake_mark(),
add a wake handler in futex_q. No extra data is associated with the
handler outside of struct futex_q itself. futex_wake_mark() is defined as
the standard wakeup helper, now set through futex_q_init like other
defaults.
Normal sync futex waiting relies on wake_q holding tasks that should
be woken up. This is what futex_wake_mark() does, it'll unqueue the
futex and add the associated task to the wake queue. For async usage of
futex waiting, rather than having tasks sleeping on the futex, we'll
need to deal with a futex wake differently. For the planned io_uring
case, that means posting a completion event for the task in question.
Having a definable wake handler can help support that use case.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
We need this for validating the futex2 flags outside of the normal
futex syscalls.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In order to support mixed size requeue, add a second flags argument to
the internal futex_requeue() function.
No functional change intended.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105248.396780136@noisy.programming.kicks-ass.net
To complement sys_futex_waitv()/wake(), add sys_futex_wait(). This
syscall implements what was previously known as FUTEX_WAIT_BITSET
except it uses 'unsigned long' for the value and bitmask arguments,
takes timespec and clockid_t arguments for the absolute timeout and
uses FUTEX2 flags.
The 'unsigned long' allows FUTEX2_SIZE_U64 on 64bit platforms.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20230921105248.164324363@noisy.programming.kicks-ass.net
The current semantics for futex_wake() are a bit loose, specifically
asking for 0 futexes to be woken actually gets you 1.
Adding a !nr check to sys_futex_wake() makes that it would return 0
for unaligned futex words, because that check comes in the shared
futex_wake() function. Adding the !nr check there, would affect the
legacy sys_futex() semantics.
Hence frob a flag :-(
Suggested-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105248.048643656@noisy.programming.kicks-ass.net
Ensure the futex value fits in the given futex size. Since this adds a
constraint to an existing syscall, it might possibly change behaviour.
Currently the value would be truncated to a u32 and any high bits
would get silently lost.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105247.828934099@noisy.programming.kicks-ass.net
Futex has 3 sets of flags:
- legacy futex op bits
- futex2 flags
- internal flags
Add a few helpers to convert from the API flags into the internal
flags.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/r/20230921105247.722140574@noisy.programming.kicks-ass.net
Now that all architectures have a working futex implementation in any
configuration, remove the runtime detection code.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Acked-by: Vineet Gupta <vgupta@kernel.org>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20211026100432.1730393-2-arnd@kernel.org
Mike reported that rcuwait went walk-about and is causing failures on
the PREEMPT_RT builds, restore it.
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Add support to wait on multiple futexes. This is the interface
implemented by this syscall:
futex_waitv(struct futex_waitv *waiters, unsigned int nr_futexes,
unsigned int flags, struct timespec *timeout, clockid_t clockid)
struct futex_waitv {
__u64 val;
__u64 uaddr;
__u32 flags;
__u32 __reserved;
};
Given an array of struct futex_waitv, wait on each uaddr. The thread
wakes if a futex_wake() is performed at any uaddr. The syscall returns
immediately if any waiter has *uaddr != val. *timeout is an optional
absolute timeout value for the operation. This syscall supports only
64bit sized timeout structs. The flags argument of the syscall should be
empty, but it can be used for future extensions. Flags for shared
futexes, sizes, etc. should be used on the individual flags of each
waiter.
__reserved is used for explicit padding and should be 0, but it might be
used for future extensions. If the userspace uses 32-bit pointers, it
should make sure to explicitly cast it when assigning to waitv::uaddr.
Returns the array index of one of the woken futexes. There’s no given
information of how many were woken, or any particular attribute of it
(if it’s the first woken, if it is of the smaller index...).
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210923171111.300673-17-andrealmeid@collabora.com
We need to make sure that all requeue operations take the hash bucket
locks in the same order to avoid deadlock. Simplify the current
double_lock_hb implementation by making sure hb1 is always the
"smallest" bucket to avoid extra checks.
[André: Add commit description]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-16-andrealmeid@collabora.com
Move the wait/wake bits into their own file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-15-andrealmeid@collabora.com
Move all the requeue bits into their own file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-14-andrealmeid@collabora.com
Move the PI futex implementation into it's own file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-10-andrealmeid@collabora.com
Put the syscalls in their own little file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-3-andrealmeid@collabora.com
