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Diffstat (limited to '')
| -rw-r--r-- | debian/patches-rt/0093-printk-Wait-for-all-reserved-records-with-pr_flush.patch | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/debian/patches-rt/0093-printk-Wait-for-all-reserved-records-with-pr_flush.patch b/debian/patches-rt/0093-printk-Wait-for-all-reserved-records-with-pr_flush.patch new file mode 100644 index 000000000..661aea210 --- /dev/null +++ b/debian/patches-rt/0093-printk-Wait-for-all-reserved-records-with-pr_flush.patch @@ -0,0 +1,170 @@ +From: John Ogness <john.ogness@linutronix.de> +Date: Mon, 6 Nov 2023 14:59:55 +0000 +Subject: [PATCH 093/134] printk: Wait for all reserved records with pr_flush() +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz + +Currently pr_flush() will only wait for records that were +available to readers at the time of the call (using +prb_next_seq()). But there may be more records (non-finalized) +that have following finalized records. pr_flush() should wait +for these to print as well. Particularly because any trailing +finalized records may be the messages that the calling context +wants to ensure are printed. + +Add a new ringbuffer function prb_next_reserve_seq() to return +the sequence number following the most recently reserved record. +This guarantees that pr_flush() will wait until all current +printk() messages (completed or in progress) have been printed. + +Fixes: 3b604ca81202 ("printk: add pr_flush()") +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/printk.c | 2 + kernel/printk/printk_ringbuffer.c | 113 ++++++++++++++++++++++++++++++++++++++ + kernel/printk/printk_ringbuffer.h | 1 + 3 files changed, 115 insertions(+), 1 deletion(-) + +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -3756,7 +3756,7 @@ static bool __pr_flush(struct console *c + + might_sleep(); + +- seq = prb_next_seq(prb); ++ seq = prb_next_reserve_seq(prb); + + /* Flush the consoles so that records up to @seq are printed. */ + console_lock(); +--- a/kernel/printk/printk_ringbuffer.c ++++ b/kernel/printk/printk_ringbuffer.c +@@ -1986,6 +1986,119 @@ u64 prb_first_seq(struct printk_ringbuff + return seq; + } + ++/** ++ * prb_next_reserve_seq() - Get the sequence number after the most recently ++ * reserved record. ++ * ++ * @rb: The ringbuffer to get the sequence number from. ++ * ++ * This is the public function available to readers to see what sequence ++ * number will be assigned to the next reserved record. ++ * ++ * Note that depending on the situation, this value can be equal to or ++ * higher than the sequence number returned by prb_next_seq(). ++ * ++ * Context: Any context. ++ * Return: The sequence number that will be assigned to the next record ++ * reserved. ++ */ ++u64 prb_next_reserve_seq(struct printk_ringbuffer *rb) ++{ ++ struct prb_desc_ring *desc_ring = &rb->desc_ring; ++ unsigned long last_finalized_id; ++ atomic_long_t *state_var; ++ u64 last_finalized_seq; ++ unsigned long head_id; ++ struct prb_desc desc; ++ unsigned long diff; ++ struct prb_desc *d; ++ int err; ++ ++ /* ++ * It may not be possible to read a sequence number for @head_id. ++ * So the ID of @last_finailzed_seq is used to calculate what the ++ * sequence number of @head_id will be. ++ */ ++ ++try_again: ++ last_finalized_seq = desc_last_finalized_seq(rb); ++ ++ /* ++ * @head_id is loaded after @last_finalized_seq to ensure that it is ++ * at or beyond @last_finalized_seq. ++ * ++ * Memory barrier involvement: ++ * ++ * If desc_last_finalized_seq:A reads from ++ * desc_update_last_finalized:A, then ++ * prb_next_reserve_seq:A reads from desc_reserve:D. ++ * ++ * Relies on: ++ * ++ * RELEASE from desc_reserve:D to desc_update_last_finalized:A ++ * matching ++ * ACQUIRE from desc_last_finalized_seq:A to prb_next_reserve_seq:A ++ * ++ * Note: desc_reserve:D and desc_update_last_finalized:A can be ++ * different CPUs. However, the desc_update_last_finalized:A CPU ++ * (which performs the release) must have previously seen ++ * desc_read:C, which implies desc_reserve:D can be seen. ++ */ ++ head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_next_reserve_seq:A) */ ++ ++ d = to_desc(desc_ring, last_finalized_seq); ++ state_var = &d->state_var; ++ ++ /* Extract the ID, used to specify the descriptor to read. */ ++ last_finalized_id = DESC_ID(atomic_long_read(state_var)); ++ ++ /* Ensure @last_finalized_id is correct. */ ++ err = desc_read_finalized_seq(desc_ring, last_finalized_id, last_finalized_seq, &desc); ++ ++ if (err == -EINVAL) { ++ if (last_finalized_seq == 0) { ++ /* ++ * @last_finalized_seq still contains its initial ++ * value. Probably no record has been finalized yet. ++ * This means the ringbuffer is not yet full and the ++ * @head_id value can be used directly (subtracting ++ * off the id value corresponding to seq=0). ++ */ ++ ++ /* ++ * Because of hack#2 of the bootstrapping phase, the ++ * @head_id initial value must be handled separately. ++ */ ++ if (head_id == DESC0_ID(desc_ring->count_bits)) ++ return 0; ++ ++ /* ++ * The @head_id is initialized such that the first ++ * increment will yield the first record (seq=0). ++ * Therefore use the initial value +1 as the base to ++ * subtract from @head_id. ++ */ ++ last_finalized_id = DESC0_ID(desc_ring->count_bits) + 1; ++ } else { ++ /* Record must have been overwritten. Try again. */ ++ goto try_again; ++ } ++ } ++ ++ /* ++ * @diff is the number of records beyond the last record available ++ * to readers. ++ */ ++ diff = head_id - last_finalized_id; ++ ++ /* ++ * @head_id points to the most recently reserved record, but this ++ * function returns the sequence number that will be assigned to the ++ * next (not yet reserved) record. Thus +1 is needed. ++ */ ++ return (last_finalized_seq + diff + 1); ++} ++ + /* + * Non-blocking read of a record. + * +--- a/kernel/printk/printk_ringbuffer.h ++++ b/kernel/printk/printk_ringbuffer.h +@@ -395,6 +395,7 @@ bool prb_read_valid_info(struct printk_r + u64 prb_first_seq(struct printk_ringbuffer *rb); + u64 prb_first_valid_seq(struct printk_ringbuffer *rb); + u64 prb_next_seq(struct printk_ringbuffer *rb); ++u64 prb_next_reserve_seq(struct printk_ringbuffer *rb); + + #ifdef CONFIG_64BIT + |