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uprobes: simplify xol_take_insn_slot() and its caller

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The do / while (slot_nr >= UINSNS_PER_PAGE) loop in xol_take_insn_slot()
makes no sense, the checked condition is always true. Change this code
to use the "for (;;)" loop, this way we do not need to change slot_nr if
test_and_set_bit() fails.

Also, kill the unnecessary xol_vaddr != NULL check in xol_get_insn_slot(),
xol_take_insn_slot() never returns NULL.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240929144244.GA9480@redhat.com
This commit is contained in:
Oleg Nesterov 2024-09-29 16:42:44 +02:00 committed by Peter Zijlstra
parent 430af825ba
commit 6ffe8c7d87
1 changed files with 4 additions and 13 deletions
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17
kernel/events/uprobes.c
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@ -1628,25 +1628,20 @@ void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
*/
static unsigned long xol_take_insn_slot(struct xol_area *area)
{
unsigned long slot_addr;
int slot_nr;
unsigned int slot_nr;
do {
for (;;) {
slot_nr = find_first_zero_bit(area->bitmap, UINSNS_PER_PAGE);
if (slot_nr < UINSNS_PER_PAGE) {
if (!test_and_set_bit(slot_nr, area->bitmap))
break;
slot_nr = UINSNS_PER_PAGE;
continue;
}
wait_event(area->wq, (atomic_read(&area->slot_count) < UINSNS_PER_PAGE));
} while (slot_nr >= UINSNS_PER_PAGE);
}
slot_addr = area->vaddr + (slot_nr * UPROBE_XOL_SLOT_BYTES);
atomic_inc(&area->slot_count);
return slot_addr;
return area->vaddr + slot_nr * UPROBE_XOL_SLOT_BYTES;
}
/*
@ -1663,12 +1658,8 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
return 0;
xol_vaddr = xol_take_insn_slot(area);
if (unlikely(!xol_vaddr))
return 0;
arch_uprobe_copy_ixol(area->page, xol_vaddr,
&uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
return xol_vaddr;
}