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Allow dcons(4) to be unloaded when loaded as a module.

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When the module is unloaded, the tty devices are destroyed.  That requires
implementing the tsw_free callback to avoid a panic.  This driver requires
no particular cleanup to be done from the callback, but the module itself
must remain in memory until the deferred tsw_free callbacks are invoked.
These changes implement that by incrementing a reference count variable in
the detach routine, and decrementing it in the tsw_free callback.  The
MOD_UNLOAD event handler doesn't return until the count drops to zero.

PR: 237758
This commit is contained in:
Ian Lepore 2019-05-10 02:30:16 +00:00
parent afb7737237
commit 0eba88cf91
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=347422
1 changed files with 18 additions and 0 deletions
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18
sys/dev/dcons/dcons_os.c
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@ -52,6 +52,7 @@
#include <sys/proc.h>
#include <sys/ucred.h>
#include <machine/atomic.h>
#include <machine/bus.h>
#include <dev/dcons/dcons.h>
@ -135,12 +136,16 @@ extern struct gdb_dbgport *gdb_cur;
#endif
static tsw_outwakeup_t dcons_outwakeup;
static tsw_free_t dcons_free;
static struct ttydevsw dcons_ttydevsw = {
.tsw_flags = TF_NOPREFIX,
.tsw_outwakeup = dcons_outwakeup,
.tsw_free = dcons_free,
};
static int dcons_close_refs;
#if (defined(GDB) || defined(DDB))
static int
dcons_check_break(struct dcons_softc *dc, int c)
@ -197,6 +202,14 @@ dcons_os_putc(struct dcons_softc *dc, int c)
bus_dmamap_sync(dg.dma_tag, dg.dma_map, BUS_DMASYNC_PREWRITE);
}
static void
dcons_free(void *xsc __unused)
{
/* Our deferred free has arrived, now we're waiting for one fewer. */
atomic_subtract_rel_int(&dcons_close_refs, 1);
}
static void
dcons_outwakeup(struct tty *tp)
{
@ -396,6 +409,8 @@ dcons_detach(int port)
dc = &sc[port];
tp = dc->tty;
/* tty_rel_gone() schedules a deferred free callback, count it. */
atomic_add_int(&dcons_close_refs, 1);
tty_lock(tp);
tty_rel_gone(tp);
@ -430,6 +445,9 @@ dcons_modevent(module_t mode, int type, void *data)
contigfree(dg.buf, DCONS_BUF_SIZE, M_DEVBUF);
}
/* Wait for tty deferred free callbacks to complete. */
while (atomic_load_acq_int(&dcons_close_refs) > 0)
pause_sbt("dcunld", mstosbt(50), mstosbt(10), 0);
break;
case MOD_SHUTDOWN:
#if 0 /* Keep connection after halt */