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[kernel] Prevent potential hang on 16550A UART by loop-reading FIFO on each interrupt #2624

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Merged
ghaerr merged 2 commits into from
Feb 21, 2026
Merged

[kernel] Prevent potential hang on 16550A UART by loop-reading FIFO on each interrupt #2624

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2082e13
[kernel] Prevent potential hang on 16550A UART by loop-reading FIFO e…
ghaerr Feb 20, 2026
942b876
Remove ASM instruction by reusing BX value
ghaerr Feb 20, 2026
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26 changes: 17 additions & 9 deletions elks/arch/i86/drivers/char/serfast.S
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@
// struct ch_queue *q = &sp->tty->inq;
// unsigned char c;
//
// do {
// c = INB(sp->io + UART_RX); // Read received data
// if (q->len < q->size) {
// q->base[q->head] = c;
Expand All @@ -36,6 +37,7 @@
// }
// if (c == 03) // assumes VINTR = ^C and byte queued anyways
// sp->intrchar = c;
// } while (INB(sp->io + UART_LSR) & UART_LSR_DR);
// }

//
Expand All @@ -62,26 +64,32 @@ common_entry:
mov %cx,%bx // bx = sp = &ports[n]
mov (%bx),%si // si = q = &sp->tty->inq
mov 0x4(%bx),%dx // dx = sp->io + UART_RX
in (%dx),%al
0: in (%dx),%al // do {
mov %al,%dl // dl = c = INB(sp->io+UART_RX)
mov (%si),%ax // ax = q->len
cmp 0x2(%si),%ax // if (ax >= q->size)
jge 2f
mov 0x4(%si),%bx // bx = q->head
mov 0x8(%si),%di // di = q->base
mov %dl,(%bx,%di) // q->base[q->head] = c
mov 0x4(%si),%ax // ax = q->head
inc %ax
mov %ax,0x4(%si) // ++q->head
cmp 0x2(%si),%ax // if (q->size < q->head)
inc %bx
mov %bx,0x4(%si) // ++q->head
cmp 0x2(%si),%bx // if (q->size < q->head)
jl 1f
movw $0x0,0x4(%si) // q->head = 0
1: incw (%si)
2: cmp $0x3,%dl // if (c == 03)
1: incw (%si) // q->len++
2: mov %cx,%bx // bx = sp
cmp $0x3,%dl // if (c == 03)
jne 3f
mov %cx,%bx // bx = sp
movw $0x3,2(%bx) // sp->intrchar = c
3: pop %di
3: mov 0x4(%bx),%dx // dx = sp->io
add $5,%dx // dx = sp->io + UART_LSR
in (%dx),%al // al = INB(sp->io + UART_LSR)
test $1,%al // while (al & UART_LSR_DR)
jz 4f
sub $5,%dx // dx = sp->io + UART_RX
jmp 0b
4: pop %di
pop %si

mov $0x20,%al // EOI on primary controller
Expand Down
4 changes: 2 additions & 2 deletions elks/arch/i86/drivers/char/serial-8250.c
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Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,7 @@ static void flush_input(register struct serial_info *sp)
#endif
}

static int rs_probe(register struct serial_info *sp)
static int INITPROC rs_probe(register struct serial_info *sp)
{
int status, type;
unsigned char scratch;
Expand Down Expand Up @@ -479,7 +479,7 @@ static int rs_ioctl(struct tty *tty, int cmd, char *arg)
return retval;
}

static void rs_init(void)
static void INITPROC rs_init(void)
{
register struct serial_info *sp = ports;
register struct tty *tty = ttys + NR_CONSOLES;
Expand Down
3 changes: 3 additions & 0 deletions elks/arch/i86/mm/malloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -291,6 +291,9 @@ static int set_brk(segoff_t brk, int increment)
stacklow = current->t_begstack - current->t_minstack;
if (newbrk > stacklow) {
printk("(%P)SBRK %d FAIL, OUT OF HEAP SPACE\n", increment);
/*printk("BEGSTK %x MINSTK %x LOWSTK %x NEWBRK %x CURBRK %x\n",
current->t_begstack, current->t_minstack, stacklow, newbrk,
current->t_endbrk);*/
return -ENOMEM;
}
if (newbrk > current->t_regs.sp) {
Expand Down