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kernel/smp: arch/x86_64: Address race with CPU migration

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Use of the _current_cpu pointer cannot be done safely in a preemptible
context.  If a thread is preempted and migrates to another CPU, the
old CPU record will be wrong.

Add a validation assert to the expression that catches incorrect
usages, and fix up the spots where it was wrong (most important being
a few uses of _current outside of locks, and the arch_is_in_isr()
implementation).

Note that the resulting _current expression now requires locking and
is going to be somewhat slower.  Longer term it's going to be better
to augment the arch API to allow SMP architectures to implement a
faster "get current thread pointer" action than this default.

Note also that this change means that "_current" is no longer
expressible as an lvalue (long ago, it was just a static variable), so
the places where it gets assigned now assign to _current_cpu->current
instead.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2020-02-06 13:39:52 -08:00 • committed by Anas Nashif
commit eefd3daa81
7 changed files with 51 additions and 12 deletions
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12
include/kernel_structs.h
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@ -195,8 +195,16 @@ typedef struct z_kernel _kernel_t;
extern struct z_kernel _kernel;
#ifdef CONFIG_SMP
#define _current_cpu (arch_curr_cpu())
#define _current (arch_curr_cpu()->current)
/* True if the current context can be preempted and migrated to
* another SMP CPU.
*/
bool z_smp_cpu_mobile(void);
#define _current_cpu ({ __ASSERT_NO_MSG(!z_smp_cpu_mobile()); \
arch_curr_cpu(); })
#define _current k_current_get()
#else
#define _current_cpu (&_kernel.cpus[0])
#define _current _kernel.current