Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk v2 6/9] printk: Wait for all reserved records with pr_flush() | Date | Mon, 6 Nov 2023 22:13:27 +0106 |
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Currently pr_flush() will only wait for records that were available to readers at the time of the call. But there may be more records (non-finalized) with 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.
Fixes: 3b604ca81202 ("printk: add pr_flush()") Signed-off-by: John Ogness <john.ogness@linutronix.de> --- kernel/printk/printk.c | 2 +- kernel/printk/printk_ringbuffer.c | 96 +++++++++++++++++++++++++++++++ kernel/printk/printk_ringbuffer.h | 1 + 3 files changed, 98 insertions(+), 1 deletion(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 82dc2c7949b7..f3a7f5a6f6f8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3755,7 +3755,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre 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(); diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 7c121fd68330..dc83569d3a3a 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -2012,6 +2012,102 @@ static u64 prb_first_seq(struct printk_ringbuffer *rb) 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(desc_ring); + + /* + * @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 its initial value). + * + * 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; + + last_finalized_id = DESC0_ID(desc_ring->count_bits) + 1; + } else { + /* Record must have been overwritten. Try again. */ + goto try_again; + } + } + + diff = head_id - last_finalized_id; + + return (last_finalized_seq + diff); +} + /* * Non-blocking read of a record. * diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h index 5c09061433f3..b48b44ecbe6d 100644 --- a/kernel/printk/printk_ringbuffer.h +++ b/kernel/printk/printk_ringbuffer.h @@ -394,5 +394,6 @@ bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, 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); #endif /* _KERNEL_PRINTK_RINGBUFFER_H */ -- 2.39.2
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