On 2019/05/29 0:03, Petr Mladek wrote: >> But is context dependent buffer large enough to hold SysRq-t output? >> I think that only main logbuf can become large enough to hold SysRq-t output. > > SysRq messages are stored directly into the main log buffer. > > The limited per-CPU buffers are needed only in printk_safe > and NMI context. We discussed it here because KERN_UNSUPPRESSED > allows to pass the information even from this context. > >> We can add KERN_UNSUPPRESSED to SysRq's header line. But I don't think >> that we can automatically add KERN_UNSUPPRESSED to SysRq's body lines >> based on some context information. If we want to avoid manipulating >> console_loglevel, we need to think about how to make sure that >> KERN_UNSUPPRESSED is added to all lines from such context without >> overflowing capacity of that buffer. > > We could set this context in printk_context per-CPU variable. > > Then we could easily add the set per-message flag in > vprintk_store() for the normal/atomic context. And we > could store an extra KERN_UNSUPPRESSED in printk_safe_log_store() > for printk_safe and NMI context.
Now I got what you are trying to do. Borrow per-CPU printk_context flags for automatically prefixing KERN_UNSUPPRESSED, based on an assumption that any message sent during that per-CPU printk_context flag set is important enough. Then, what we need to be careful is nesting of setting/clearing of that flag, for NMI handler might be called during SysRq operation is in progress. We unconditionally prefix KERN_UNSUPPRESSED if NMI?
