On Sat, Jul 13, 2019 at 9:10 AM Sergey Senozhatsky <[email protected]> wrote: > > On (07/12/19 17:54), Konstantin Khlebnikov wrote: > > Function kmsg_dump could be invoked from NMI context intentionally or > > accidentally because it is called at various oops/panic paths. > > Kernel message dumpers are not ready to work in NMI context right now. > > They could deadlock on lockbuf_lock or break internal structures. > > Hmm. > printk()-s from NMI go through per-CPU printk_safe/nmi - a bunch of > lockless buffers which is supposed to deal with printk() deadlocks, > including NMI printk()-s. > > include/linux/hardirq.h > > #define nmi_enter() > ... > printk_nmi_enter(); > ... > > #define nmi_exit() > ... > printk_nmi_exit(); > ... > > So we are not really supposed to deadlock.
Yep printk() can deal with NMI, but kmsg_dump() is a different beast. It reads printk buffer and saves content into persistent storage like ACPI ERST. > > -ss
