Messages in this thread | | | Date | Thu, 19 May 2022 16:37:38 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 20/21] context_tracking: Convert state to atomic_t |
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On Wed, May 18, 2022 at 05:09:55PM +0200, nicolas saenz julienne wrote: > On Tue, 2022-05-03 at 12:00 +0200, Frederic Weisbecker wrote: > > [...] > > > +/** > > + * ct_state() - return the current context tracking state if known > > + * > > + * Returns the current cpu's context tracking state if context tracking > > + * is enabled. If context tracking is disabled, returns > > + * CONTEXT_DISABLED. This should be used primarily for debugging. > > + */ > > +static __always_inline int ct_state(void) > > +{ > > + int ret; > > + > > + if (!context_tracking_enabled()) > > + return CONTEXT_DISABLED; > > + > > + preempt_disable(); > > + ret = __ct_state(); > > + preempt_enable(); > > + > > + return ret; > > +} > > + > > I can't see any use for this function with preemption enabled. You can't trust > the data due to CPU migration and it could be a source of bugs in the future. > Wouldn't it make more sense to move the burden into the callers? They all DTRT, > plus, this_cpu_ptr() will spew warnings if someone shows up and doesn't comply.
I believe syscall_exit_to_user_mode_prepare() has preemption enabled. Then it's ok if we are scheduled away right before the check, it still applies on any CPU.
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