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printk: nobkl: Add emit function and callback functions for atomic printing

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Implement an emit function for non-BKL consoles to output printk
messages. It utilizes the lockless printk_get_next_message() and
console_prepend_dropped() functions to retrieve/build the output
message. The emit function includes the required safety points to
check for handover/takeover and calls a new write_atomic callback
of the console driver to output the message. It also includes proper
handling for updating the non-BKL console sequence number.

Co-developed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
This commit is contained in:
Thomas Gleixner
2022-09-11 00:28:10 +02:00
committed by Sebastian Andrzej Siewior
parent d803bcd90a
commit fdf2dc1e54
4 changed files with 142 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/linux/console.h
+8
View File
@@ -251,10 +251,12 @@ struct printk_buffers;
* @newseq: The sequence number for progress
* @prio: Priority of the context
* @pbufs: Pointer to the text buffer for this context
* @dropped: Dropped counter for the current context
* @thread: The acquire is printk thread context
* @hostile: Hostile takeover requested. Cleared on normal
* acquire or friendly handover
* @spinwait: Spinwait on acquire if possible
* @backlog: Ringbuffer has pending records
*/
struct cons_context {
struct console *console;
@@ -267,9 +269,11 @@ struct cons_context {
unsigned int spinwait_max_us;
enum cons_prio prio;
struct printk_buffers *pbufs;
unsigned long dropped;
unsigned int thread : 1;
unsigned int hostile : 1;
unsigned int spinwait : 1;
unsigned int backlog : 1;
};
/**
@@ -311,6 +315,7 @@ struct cons_context_data;
* @atomic_state: State array for NOBKL consoles; real and handover
* @atomic_seq: Sequence for record tracking (32bit only)
* @thread_pbufs: Pointer to thread private buffer
* @write_atomic: Write callback for atomic context
* @pcpu_data: Pointer to percpu context data
*/
struct console {
@@ -338,6 +343,9 @@ struct console {
atomic_t __private atomic_seq;
#endif
struct printk_buffers *thread_pbufs;
bool (*write_atomic)(struct console *con, struct cons_write_context *wctxt);
struct cons_context_data __percpu *pcpu_data;
};
kernel/printk/internal.h
+10
View File
@@ -134,4 +134,14 @@ struct cons_context_data {
struct printk_buffers pbufs;
};
bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
bool is_extended, bool may_supress);
#ifdef CONFIG_PRINTK
void console_prepend_dropped(struct printk_message *pmsg,
unsigned long dropped);
#endif
bool other_cpu_in_panic(void);
kernel/printk/printk.c
+5 -7
View File
@@ -713,9 +713,6 @@ out:
return len;
}
static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
bool is_extended, bool may_supress);
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
atomic64_t seq;
@@ -2769,7 +2766,7 @@ static void __console_unlock(void)
* If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
*/
#ifdef CONFIG_PRINTK
static void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
{
struct printk_buffers *pbufs = pmsg->pbufs;
const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
@@ -2801,7 +2798,8 @@ static void console_prepend_dropped(struct printk_message *pmsg, unsigned long d
pmsg->outbuf_len += len;
}
#else
#define console_prepend_dropped(pmsg, dropped)
static inline void console_prepend_dropped(struct printk_message *pmsg,
unsigned long dropped) { }
#endif /* CONFIG_PRINTK */
/*
@@ -2823,8 +2821,8 @@ static void console_prepend_dropped(struct printk_message *pmsg, unsigned long d
* of @pmsg are valid. (See the documentation of struct printk_message
* for information about the @pmsg fields.)
*/
static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
bool is_extended, bool may_suppress)
bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
bool is_extended, bool may_suppress)
{
static int panic_console_dropped;
kernel/printk/printk_nobkl.c
+119 -2
View File
@@ -317,7 +317,7 @@ static void cons_context_set_seq(struct cons_context *ctxt)
* invalid. Caller has to reacquire the console.
*/
#ifdef CONFIG_64BIT
static bool __maybe_unused cons_seq_try_update(struct cons_context *ctxt)
static bool cons_seq_try_update(struct cons_context *ctxt)
{
struct console *con = ctxt->console;
struct cons_state old;
@@ -346,7 +346,7 @@ static bool __maybe_unused cons_seq_try_update(struct cons_context *ctxt)
}
#else
static bool cons_release(struct cons_context *ctxt);
static bool __maybe_unused cons_seq_try_update(struct cons_context *ctxt)
static bool cons_seq_try_update(struct cons_context *ctxt)
{
struct console *con = ctxt->console;
struct cons_state state;
@@ -1089,6 +1089,123 @@ bool console_exit_unsafe(struct cons_write_context *wctxt)
}
EXPORT_SYMBOL_GPL(console_exit_unsafe);
/**
* cons_get_record - Fill the buffer with the next pending ringbuffer record
* @wctxt: The write context which will be handed to the write function
*
* Returns: True if there are records available. If the next record should
* be printed, the output buffer is filled and @wctxt->outbuf
* points to the text to print. If @wctxt->outbuf is NULL after
* the call, the record should not be printed but the caller must
* still update the console sequence number.
*
* False means that there are no pending records anymore and the
* printing can stop.
*/
static bool cons_get_record(struct cons_write_context *wctxt)
{
struct cons_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
struct console *con = ctxt->console;
bool is_extended = console_srcu_read_flags(con) & CON_EXTENDED;
struct printk_message pmsg = {
.pbufs = ctxt->pbufs,
};
if (!printk_get_next_message(&pmsg, ctxt->newseq, is_extended, true))
return false;
ctxt->newseq = pmsg.seq;
ctxt->dropped += pmsg.dropped;
if (pmsg.outbuf_len == 0) {
wctxt->outbuf = NULL;
} else {
if (ctxt->dropped && !is_extended)
console_prepend_dropped(&pmsg, ctxt->dropped);
wctxt->outbuf = &pmsg.pbufs->outbuf[0];
}
wctxt->len = pmsg.outbuf_len;
return true;
}
/**
* cons_emit_record - Emit record in the acquired context
* @wctxt: The write context that will be handed to the write function
*
* Returns: False if the operation was aborted (takeover or handover).
* True otherwise
*
* When false is returned, the caller is not allowed to touch console state.
* The console is owned by someone else. If the caller wants to print more
* it has to reacquire the console first.
*
* When true is returned, @wctxt->ctxt.backlog indicates whether there are
* still records pending in the ringbuffer,
*/
static int __maybe_unused cons_emit_record(struct cons_write_context *wctxt)
{
struct cons_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
struct console *con = ctxt->console;
bool done = false;
/*
* @con->dropped is not protected in case of hostile takeovers so
* the update below is racy. Annotate it accordingly.
*/
ctxt->dropped = data_race(READ_ONCE(con->dropped));
/* Fill the output buffer with the next record */
ctxt->backlog = cons_get_record(wctxt);
if (!ctxt->backlog)
return true;
/* Safety point. Don't touch state in case of takeover */
if (!console_can_proceed(wctxt))
return false;
/* Counterpart to the read above */
WRITE_ONCE(con->dropped, ctxt->dropped);
/*
* In case of skipped records, Update sequence state in @con.
*/
if (!wctxt->outbuf)
goto update;
/* Tell the driver about potential unsafe state */
wctxt->unsafe = ctxt->state.unsafe;
if (!ctxt->thread && con->write_atomic) {
done = con->write_atomic(con, wctxt);
} else {
cons_release(ctxt);
WARN_ON_ONCE(1);
return false;
}
/* If not done, the write was aborted due to takeover */
if (!done)
return false;
/* If there was a dropped message, it has now been output. */
if (ctxt->dropped) {
ctxt->dropped = 0;
/* Counterpart to the read above */
WRITE_ONCE(con->dropped, ctxt->dropped);
}
update:
ctxt->newseq++;
/*
* The sequence update attempt is not part of console_release()
* because in panic situations the console is not released by
* the panic CPU until all records are written. On 32bit the
* sequence is separate from state anyway.
*/
return cons_seq_try_update(ctxt);
}
/**
* cons_nobkl_init - Initialize the NOBKL console specific data
* @con: Console to initialize