diff options
| -rw-r--r-- | include/linux/console.h | 19 | ||||
| -rw-r--r-- | kernel/printk/nbcon.c | 47 |
2 files changed, 48 insertions, 18 deletions
diff --git a/include/linux/console.h b/include/linux/console.h index d17f1f525bec..5f17321ed962 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -186,6 +186,8 @@ static inline void con_debug_leave(void) { } * printing callbacks must not be called. * @CON_NBCON: Console can operate outside of the legacy style console_lock * constraints. + * @CON_NBCON_ATOMIC_UNSAFE: The write_atomic() callback is not safe and is + * therefore only used by nbcon_atomic_flush_unsafe(). */ enum cons_flags { CON_PRINTBUFFER = BIT(0), @@ -197,6 +199,7 @@ enum cons_flags { CON_EXTENDED = BIT(6), CON_SUSPENDED = BIT(7), CON_NBCON = BIT(8), + CON_NBCON_ATOMIC_UNSAFE = BIT(9), }; /** @@ -608,6 +611,7 @@ extern void nbcon_write_context_set_buf(struct nbcon_write_context *wctxt, extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt); +extern bool nbcon_allow_unsafe_takeover(void); extern bool nbcon_kdb_try_acquire(struct console *con, struct nbcon_write_context *wctxt); extern void nbcon_kdb_release(struct nbcon_write_context *wctxt); @@ -627,9 +631,18 @@ static inline bool console_is_usable(struct console *con, short flags, bool use_ return false; if (flags & CON_NBCON) { - /* The write_atomic() callback is optional. */ - if (use_atomic && !con->write_atomic) - return false; + if (use_atomic) { + /* The write_atomic() callback is optional. */ + if (!con->write_atomic) + return false; + + /* + * An unsafe write_atomic() callback is only usable + * when unsafe takeovers are allowed. + */ + if ((flags & CON_NBCON_ATOMIC_UNSAFE) && !nbcon_allow_unsafe_takeover()) + return false; + } /* * For the !use_atomic case, @printk_kthreads_running is not diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index fdd1cbebe77d..90412c2b2961 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1408,6 +1408,26 @@ enum nbcon_prio nbcon_get_default_prio(void) return NBCON_PRIO_NORMAL; } +/* + * Track if it is allowed to perform unsafe hostile takeovers of console + * ownership. When true, console drivers might perform unsafe actions while + * printing. It is externally available via nbcon_allow_unsafe_takeover(). + */ +static bool panic_nbcon_allow_unsafe_takeover; + +/** + * nbcon_allow_unsafe_takeover - Check if unsafe console takeovers are allowed + * + * Return: True, when it is permitted to perform unsafe console printing + * + * This is also used by console_is_usable() to determine if it is allowed to + * call write_atomic() callbacks flagged as unsafe (CON_NBCON_ATOMIC_UNSAFE). + */ +bool nbcon_allow_unsafe_takeover(void) +{ + return panic_on_this_cpu() && panic_nbcon_allow_unsafe_takeover; +} + /** * nbcon_legacy_emit_next_record - Print one record for an nbcon console * in legacy contexts @@ -1478,7 +1498,6 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, * write_atomic() callback * @con: The nbcon console to flush * @stop_seq: Flush up until this record - * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers * * Return: 0 if @con was flushed up to @stop_seq Otherwise, error code on * failure. @@ -1497,8 +1516,7 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, * returned, it cannot be expected that the unfinalized record will become * available. */ -static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, - bool allow_unsafe_takeover) +static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) { struct nbcon_write_context wctxt = { }; struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); @@ -1507,7 +1525,7 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, ctxt->console = con; ctxt->spinwait_max_us = 2000; ctxt->prio = nbcon_get_default_prio(); - ctxt->allow_unsafe_takeover = allow_unsafe_takeover; + ctxt->allow_unsafe_takeover = nbcon_allow_unsafe_takeover(); if (!nbcon_context_try_acquire(ctxt, false)) return -EPERM; @@ -1538,15 +1556,13 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, * write_atomic() callback * @con: The nbcon console to flush * @stop_seq: Flush up until this record - * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers * * This will stop flushing before @stop_seq if another context has ownership. * That context is then responsible for the flushing. Likewise, if new records * are added while this context was flushing and there is no other context * to handle the printing, this context must also flush those records. */ -static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, - bool allow_unsafe_takeover) +static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) { struct console_flush_type ft; unsigned long flags; @@ -1561,7 +1577,7 @@ again: */ local_irq_save(flags); - err = __nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); + err = __nbcon_atomic_flush_pending_con(con, stop_seq); local_irq_restore(flags); @@ -1593,9 +1609,8 @@ again: * __nbcon_atomic_flush_pending - Flush all nbcon consoles using their * write_atomic() callback * @stop_seq: Flush up until this record - * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers */ -static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeover) +static void __nbcon_atomic_flush_pending(u64 stop_seq) { struct console *con; int cookie; @@ -1613,7 +1628,7 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeove if (nbcon_seq_read(con) >= stop_seq) continue; - nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); + nbcon_atomic_flush_pending_con(con, stop_seq); } console_srcu_read_unlock(cookie); } @@ -1629,7 +1644,7 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeove */ void nbcon_atomic_flush_pending(void) { - __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), false); + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb)); } /** @@ -1641,7 +1656,9 @@ void nbcon_atomic_flush_pending(void) */ void nbcon_atomic_flush_unsafe(void) { - __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), true); + panic_nbcon_allow_unsafe_takeover = true; + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb)); + panic_nbcon_allow_unsafe_takeover = false; } /** @@ -1848,7 +1865,7 @@ void nbcon_device_release(struct console *con) * using the legacy loop. */ if (ft.nbcon_atomic) { - __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false); + __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb)); } else if (ft.legacy_direct) { if (console_trylock()) console_unlock(); @@ -1918,5 +1935,5 @@ void nbcon_kdb_release(struct nbcon_write_context *wctxt) * The console was locked only when the write_atomic() callback * was usable. */ - __nbcon_atomic_flush_pending_con(ctxt->console, prb_next_reserve_seq(prb), false); + __nbcon_atomic_flush_pending_con(ctxt->console, prb_next_reserve_seq(prb)); } |