[Cc s390 maintainers - the lockdep is http://lkml.kernel.org/r/1570228005-24979-1-git-send-email-cai@xxxxxx Petr has explained it is a false positive http://lkml.kernel.org/r/20191007143002.l37bt2lzqtnqjqxu@xxxxxxxxxxxxxxx] On Mon 07-10-19 16:30:02, Petr Mladek wrote: [...] > I believe that it cannot really happen because: > > static int __init > sclp_console_init(void) > { > [...] > rc = sclp_rw_init(); > [...] > register_console(&sclp_console); > return 0; > } > > sclp_rw_init() is called before register_console(). And > console_unlock() will never call sclp_console_write() before > the console is registered. > > AFAIK, lockdep only compares existing chain of locks. It does > not know about console registration that would make some > code paths mutually exclusive. > > I believe that it is a false positive. I do not know how to > avoid this lockdep report. I hope that it will disappear > by deferring all printk() calls rather soon. Thanks a lot for looking into this Petr. I have also checked the code and I really fail to see why the allocation has to be done under the lock in the first place. sclp_read_sccb and sclp_init_sccb are global variables but I strongly suspect that they need a synchronization during early init, callbacks are registered only later IIUC: diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c index d2ab3f07c008..4b1c033e3255 100644 --- a/drivers/s390/char/sclp.c +++ b/drivers/s390/char/sclp.c @@ -1169,13 +1169,13 @@ sclp_init(void) unsigned long flags; int rc = 0; + sclp_read_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); + sclp_init_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); spin_lock_irqsave(&sclp_lock, flags); /* Check for previous or running initialization */ if (sclp_init_state != sclp_init_state_uninitialized) goto fail_unlock; sclp_init_state = sclp_init_state_initializing; - sclp_read_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); - sclp_init_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA); BUG_ON(!sclp_read_sccb || !sclp_init_sccb); /* Set up variables */ INIT_LIST_HEAD(&sclp_req_queue); -- Michal Hocko SUSE Labs
