Outside of the locking code itself, {read,spin,write}_can_lock() have no
users in tree. Apparmor (the last remaining user of write_can_lock()) got
moved over to lockdep by the previous patch.
This patch removes the use of {read,spin,write}_can_lock() from the
BUILD_LOCK_OPS macro, deferring to the trylock operation for testing the
lock status, and subsequently removes the unused macros altogether. They
aren't guaranteed to work in a concurrent environment and can give
incorrect results in the case of qrwlock.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1507055129-12300-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull ARC updates from Vineet Gupta:
- Support for HSDK board hosting a Quad core HS38x4 based SoC running
@1GHz (and some prerrquisite changes such as ability to scoot the
kernel code/data from start of memory map etc)
- Quite a few updates for EZChip (Mellanox) platform
- Fixes to fault/exception printing
* tag 'arc-4.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc: (26 commits)
ARC: Re-enable MMU upon Machine Check exception
ARC: Show fault information passed to show_kernel_fault_diag()
ARC: [plat-hsdk] initial port for HSDK board
ARC: mm: Decouple RAM base address from kernel link address
ARCv2: IOC: Tighten up the contraints (specifically base / size alignment)
ARC: [plat-axs103] refactor the DT fudging code
ARC: [plat-axs103] use clk driver #2: Add core pll node to DT to manage cpu clk
ARC: [plat-axs103] use clk driver #1: Get rid of platform specific cpu clk setting
ARCv2: SLC: provide a line based flush routine for debugging
ARC: Hardcode ARCH_DMA_MINALIGN to max line length we may have
ARC: [plat-eznps] handle extra aux regs #2: kernel/entry exit
ARC: [plat-eznps] handle extra aux regs #1: save/restore on context switch
ARC: [plat-eznps] avoid toggling of DPC register
ARC: [plat-eznps] Update the init sequence of aux regs per cpu.
ARC: [plat-eznps] new command line argument for HW scheduler at MTM
ARC: set boot print log level to PR_INFO
ARC: [plat-eznps] Handle user memory error same in simulation and silicon
ARC: [plat-eznps] use schd.wft instruction instead of sleep at idle task
ARC: create cpu specific version of arch_cpu_idle()
ARC: [plat-eznps] spinlock aware for MTM
...
This way when we execute "ex" during trying to hold lock we can switch to
other HW thread and utilize the core intead of just spinning on a lock.
We noticed about 10% improvement of execution time with hackbench test.
Signed-off-by: Noam Camus <noamca@mellanox.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This reverts commit e78fdfef84.
The issue was fixed in hardware in HS2.1C release and there are no known
external users of affected RTL so revert the whole delayed retry series !
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This reverts commit b89aa12c17.
The issue was fixed in hardware in HS2.1C release and there are no known
external users of affected RTL so revert the whole delayed retry series !
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This reverts commit 1097163870.
The issue was fixed in hardware in HS2.1C release and there are no known
external users of affected RTL - so revert thw whole delayed retry
series !
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
If we hold rwlock and interrupt occures we may
end up spinning on it for ever during softirq.
Note that this lock is an internal lock
and since the lock is free to be used from any context,
the lock needs to be IRQ-safe.
Below you may see an example for interrupt we get while
nl_table_lock is holding its rw->lock_mutex and we spinned
on it for ever.
The concept for the fix was taken from SPARC.
[2015-05-12 19:16:12] Stack Trace:
[2015-05-12 19:16:12] arc_unwind_core+0xb8/0x11c
[2015-05-12 19:16:12] dump_stack+0x68/0xac
[2015-05-12 19:16:12] _raw_read_lock+0xa8/0xac
[2015-05-12 19:16:12] netlink_broadcast_filtered+0x56/0x35c
[2015-05-12 19:16:12] nlmsg_notify+0x42/0xa4
[2015-05-12 19:16:13] neigh_update+0x1fe/0x44c
[2015-05-12 19:16:13] neigh_event_ns+0x40/0xa4
[2015-05-12 19:16:13] arp_process+0x46e/0x5a8
[2015-05-12 19:16:13] __netif_receive_skb_core+0x358/0x500
[2015-05-12 19:16:13] process_backlog+0x92/0x154
[2015-05-12 19:16:13] net_rx_action+0xb8/0x188
[2015-05-12 19:16:13] __do_softirq+0xda/0x1d8
[2015-05-12 19:16:14] irq_exit+0x8a/0x8c
[2015-05-12 19:16:14] arch_do_IRQ+0x6c/0xa8
[2015-05-12 19:16:14] handle_interrupt_level1+0xe4/0xf0
Signed-off-by: Noam Camus <noamc@ezchip.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
The previous commit for delayed retry of SCOND needs some fine tuning
for spin locks.
The backoff from delayed retry in conjunction with spin looping of lock
itself can potentially cause the delay counter to reach high values.
So to provide fairness to any lock operation, after a lock "seems"
available (i.e. just before first SCOND try0, reset the delay counter
back to starting value of 1
Essentially reset delay to 1 for a new spin-wait-loop-acquire cycle.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This is to workaround the llock/scond livelock
HS38x4 could get into a LLOCK/SCOND livelock in case of multiple overlapping
coherency transactions in the SCU. The exclusive line state keeps rotating
among contenting cores leading to a never ending cycle. So break the cycle
by deferring the retry of failed exclusive access (SCOND). The actual delay
needed is function of number of contending cores as well as the unrelated
coherency traffic from other cores. To keep the code simple, start off with
small delay of 1 which would suffice most cases and in case of contention
double the delay. Eventually the delay is sufficient such that the coherency
pipeline is drained, thus a subsequent exclusive access would succeed.
Link: http://lkml.kernel.org/r/1438612568-28265-1-git-send-email-vgupta@synopsys.com
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
With LLOCK/SCOND, the rwlock counter can be atomically updated w/o need
for a guarding spin lock.
This in turn elides the EXchange instruction based spinning which causes
the cacheline transition to exclusive state and concurrent spinning
across cores would cause the line to keep bouncing around.
LLOCK/SCOND based implementation is superior as spinning on LLOCK keeps
the cacheline in shared state.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Current spin_lock uses EXchange instruction to implement the atomic test
and set of lock location (reads orig value and ST 1). This however forces
the cacheline into exclusive state (because of the ST) and concurrent
loops in multiple cores will bounce the line around between cores.
Instead, use LLOCK/SCOND to implement the atomic test and set which is
better as line is in shared state while lock is spinning on LLOCK
The real motivation of this change however is to make way for future
changes in atomics to implement delayed retry (with backoff).
Initial experiment with delayed retry in atomics combined with orig
EX based spinlock was a total disaster (broke even LMBench) as
struct sock has a cache line sharing an atomic_t and spinlock. The
tight spinning on lock, caused the atomic retry to keep backing off
such that it would never finish.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
- arch_spin_lock/unlock were lacking the ACQUIRE/RELEASE barriers
Since ARCv2 only provides load/load, store/store and all/all, we need
the full barrier
- LLOCK/SCOND based atomics, bitops, cmpxchg, which return modified
values were lacking the explicit smp barriers.
- Non LLOCK/SCOND varaints don't need the explicit barriers since that
is implicity provided by the spin locks used to implement the
critical section (the spin lock barriers in turn are also fixed in
this commit as explained above
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Some ARC SMP systems lack native atomic R-M-W (LLOCK/SCOND) insns and
can only use atomic EX insn (reg with mem) to build higher level R-M-W
primitives. This includes a SystemC based SMP simulation model.
So rwlocks need to use a protecting spinlock for atomic cmp-n-exchange
operation to update reader(s)/writer count.
The spinlock operation itself looks as follows:
mov reg, 1 ; 1=locked, 0=unlocked
retry:
EX reg, [lock] ; load existing, store 1, atomically
BREQ reg, 1, rety ; if already locked, retry
In single-threaded simulation, SystemC alternates between the 2 cores
with "N" insn each based scheduling. Additionally for insn with global
side effect, such as EX writing to shared mem, a core switch is
enforced too.
Given that, 2 cores doing a repeated EX on same location, Linux often
got into a livelock e.g. when both cores were fiddling with tasklist
lock (gdbserver / hackbench) for read/write respectively as the
sequence diagram below shows:
core1 core2
-------- --------
1. spin lock [EX r=0, w=1] - LOCKED
2. rwlock(Read) - LOCKED
3. spin unlock [ST 0] - UNLOCKED
spin lock [EX r=0,w=1] - LOCKED
-- resched core 1----
5. spin lock [EX r=1] - ALREADY-LOCKED
-- resched core 2----
6. rwlock(Write) - READER-LOCKED
7. spin unlock [ST 0]
8. rwlock failed, retry again
9. spin lock [EX r=0, w=1]
-- resched core 1----
10 spinlock locked in #9, retry #5
11. spin lock [EX gets 1]
-- resched core 2----
...
...
The fix was to unlock using the EX insn too (step 7), to trigger another
SystemC scheduling pass which would let core1 proceed, eliding the
livelock.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
