From 4cfc7258f876a7feba673ac6d050f525b39cc84c Mon Sep 17 00:00:00 2001 From: John Ogness Date: Mon, 14 Sep 2020 14:39:53 +0206 Subject: printk: ringbuffer: add finalization/extension support Add support for extending the newest data block. For this, introduce a new finalization state (desc_finalized) denoting a committed descriptor that cannot be extended. Until a record is finalized, a writer can reopen that record to append new data. Reopening a record means transitioning from the desc_committed state back to the desc_reserved state. A writer can explicitly finalize a record if there is no intention of extending it. Also, records are automatically finalized when a new record is reserved. This relieves writers of needing to explicitly finalize while also making such records available to readers sooner. (Readers can only traverse finalized records.) Four new memory barrier pairs are introduced. Two of them are insignificant additions (data_realloc:A/desc_read:D and data_realloc:A/data_push_tail:B) because they are alternate path memory barriers that exactly match the purpose, pairing, and context of the two existing memory barrier pairs they provide an alternate path for. The other two new memory barrier pairs are significant additions: desc_reopen_last:A / _prb_commit:B - When reopening a descriptor, ensure the state transitions back to desc_reserved before fully trusting the descriptor data. _prb_commit:B / desc_reserve:D - When committing a descriptor, ensure the state transitions to desc_committed before checking the head ID to see if the descriptor needs to be finalized. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20200914123354.832-6-john.ogness@linutronix.de --- scripts/gdb/linux/dmesg.py | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'scripts/gdb/linux') diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py index dd8c0b95063a..bce14de5f610 100644 --- a/scripts/gdb/linux/dmesg.py +++ b/scripts/gdb/linux/dmesg.py @@ -79,6 +79,7 @@ class LxDmesg(gdb.Command): # definitions from kernel/printk/printk_ringbuffer.h desc_committed = 1 + desc_finalized = 2 desc_sv_bits = utils.get_long_type().sizeof * 8 desc_flags_shift = desc_sv_bits - 2 desc_flags_mask = 3 << desc_flags_shift @@ -98,7 +99,7 @@ class LxDmesg(gdb.Command): # skip non-committed record state = 3 & (utils.read_u64(descs, desc_off + sv_off + counter_off) >> desc_flags_shift) - if state != desc_committed: + if state != desc_committed and state != desc_finalized: if did == head_id: break did = (did + 1) & desc_id_mask -- cgit v1.2.3