Thanks for the pointer Thomas :) Regards Preeti U murthy On 07/07/2013 01:18 AM, Thomas Gleixner wrote: > On Sat, 6 Jul 2013, Preeti U Murthy wrote: > >> Hi Wang, >> >> On 07/06/2013 11:42 AM, Wang YanQing wrote: >>> On Fri, Jul 05, 2013 at 09:57:11PM +0530, Preeti U Murthy wrote: >>>> Elaborate on when deadlocks can occur when a call is made to >>>> smp_call_function_single() and its friends. This avoids ambiguity about >>>> when to use these calls. >>>> >>>> + * 2. wait = 0: This function could be called from an interrupt >>>> + * context, and can get blocked on the csd_lock(csd) below in >>>> + * "non wait cases". >>>> + * This is because the percpu copy of csd of this_cpu is used >>>> + * in non wait cases. Under such circumstances, if the previous caller >>>> + * of this function who got preempted by this interrupt has already >>>> taken >>>> + * the lock under non wait condition, it will result in deadlock. >>>> + * >>> >>> No, it will not cause deadlock, it is not mutex lock, it is busy wait, so >>> when the CSD_FLAG_LOCK be cleared, the code will go on running. >> >> A deadlock might not result, but a potential long wait in an interrupt >> context could result if the source cpu got preempted by an interrupt >> between csd_lock(csd) and generic_exec_single(), where it actually >> sends an ipi to the target cpu. > > See https://lkml.org/lkml/2013/7/5/183 and the related thread for real > deadlock scenarios. > > Thanks, > > tglx >
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