Messages in this thread Patch in this message | | | Date | Tue, 19 May 2015 00:21:23 -0700 | From | tip-bot for David Hildenbrand <> | Subject | [tip:sched/core] sched/preempt, arm/futex: Disable preemption in UP futex_atomic_op_inuser() explicitly |
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Commit-ID: 388b0e0adbc98a1b12a077dc92851a3ce016db42 Gitweb: http://git.kernel.org/tip/388b0e0adbc98a1b12a077dc92851a3ce016db42 Author: David Hildenbrand <dahi@linux.vnet.ibm.com> AuthorDate: Mon, 11 May 2015 17:52:16 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 19 May 2015 08:39:17 +0200
sched/preempt, arm/futex: Disable preemption in UP futex_atomic_op_inuser() explicitly
The !CONFIG_SMP implementation of futex_atomic_op_inuser() seems to rely on disabled preemption to guarantee mutual exclusion.
From commit e589ed23dd27 ("[ARM] 5218/1: arm: improved futex support"):
"For UP it's enough to disable preemption to ensure mutual exclusion..."
From the code itself:
"!SMP, we can work around lack of atomic ops by disabling preemption"
Let's make this explicit, to prepare for pagefault_disable() not touching preemption anymore.
Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: David.Laight@ACULAB.COM Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: airlied@linux.ie Cc: akpm@linux-foundation.org Cc: benh@kernel.crashing.org Cc: bigeasy@linutronix.de Cc: borntraeger@de.ibm.com Cc: daniel.vetter@intel.com Cc: heiko.carstens@de.ibm.com Cc: herbert@gondor.apana.org.au Cc: hocko@suse.cz Cc: hughd@google.com Cc: mst@redhat.com Cc: paulus@samba.org Cc: ralf@linux-mips.org Cc: schwidefsky@de.ibm.com Cc: yang.shi@windriver.com Link: http://lkml.kernel.org/r/1431359540-32227-12-git-send-email-dahi@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/arm/include/asm/futex.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h index 255bfd1..5eed828 100644 --- a/arch/arm/include/asm/futex.h +++ b/arch/arm/include/asm/futex.h @@ -127,7 +127,10 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr) if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))) return -EFAULT; - pagefault_disable(); /* implies preempt_disable() */ +#ifndef CONFIG_SMP + preempt_disable(); +#endif + pagefault_disable(); switch (op) { case FUTEX_OP_SET: @@ -149,7 +152,10 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr) ret = -ENOSYS; } - pagefault_enable(); /* subsumes preempt_enable() */ + pagefault_enable(); +#ifndef CONFIG_SMP + preempt_enable(); +#endif if (!ret) { switch (cmp) {
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