Commit aa5de305 authored Oct 18, 2019 by Song Liu Committed by Linus Torvalds Oct 19, 2019

kernel/events/uprobes.c: only do FOLL_SPLIT_PMD for uprobe register

Attaching uprobe to text section in THP splits the PMD mapped page table
into PTE mapped entries.  On uprobe detach, we would like to regroup PMD
mapped page table entry to regain performance benefit of THP.

However, the regroup is broken For perf_event based trace_uprobe.  This
is because perf_event based trace_uprobe calls uprobe_unregister twice
on close: first in TRACE_REG_PERF_CLOSE, then in
TRACE_REG_PERF_UNREGISTER.  The second call will split the PMD mapped
page table entry, which is not the desired behavior.

Fix this by only use FOLL_SPLIT_PMD for uprobe register case.

Add a WARN() to confirm uprobe unregister never work on huge pages, and
abort the operation when this WARN() triggers.

Link: http://lkml.kernel.org/r/20191017164223.2762148-6-songliubraving@fb.com


Fixes: 5a52c9df ("uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT")
Signed-off-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ef18a1ca

kernel/events/uprobes.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -474,14 +474,17 @@ int uprobe_write_opcode(struct arch_uprobe auprobe, struct mm_struct mm,
		struct vm_area_struct *vma;
		int ret, is_register, ref_ctr_updated = 0;
		bool orig_page_huge = false;
		unsigned int gup_flags = FOLL_FORCE;

		is_register = is_swbp_insn(&opcode);
		uprobe = container_of(auprobe, struct uprobe, arch);

		retry:
		if (is_register)
		gup_flags \|= FOLL_SPLIT_PMD;
		/* Read the page with vaddr into memory */
		ret = get_user_pages_remote(NULL, mm, vaddr, 1,
		FOLL_FORCE \| FOLL_SPLIT_PMD, &old_page, &vma, NULL);
		ret = get_user_pages_remote(NULL, mm, vaddr, 1, gup_flags,
		&old_page, &vma, NULL);
		if (ret <= 0)
		return ret;

		@@ -489,6 +492,12 @@ retry:
		if (ret <= 0)
		goto put_old;

		if (WARN(!is_register && PageCompound(old_page),
		"uprobe unregister should never work on compound page\n")) {
		ret = -EINVAL;
		goto put_old;
		}

		/* We are going to replace instruction, update ref_ctr. */
		if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
		ret = update_ref_ctr(uprobe, mm, is_register ? 1 : -1);

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