From 9f92448ceeea5326db7d114005a7e7ac03904edf Mon Sep 17 00:00:00 2001 From: Oleg Nesterov <oleg@redhat.com> Date: Sun, 29 Jul 2012 20:22:20 +0200 Subject: [PATCH] uprobes: Clean up and document write_opcode()->lock_page(old_page) The comment above write_opcode()->lock_page(old_page) tells about the race with do_wp_page(). I don't really understand which exactly race it means, but afaics this lock_page() was not enough to close all races with do_wp_page(). Anyway, since: 77fc4af1b59d uprobes: Change register_for_each_vma() to take mm->mmap_sem for writing this code is always called with ->mmap_sem held for writing, so we can forget about do_wp_page(). However, we can't simply remove this lock_page(), and the only (afaics) reason is __replace_page()->try_to_free_swap(). Nothing in write_opcode() needs it, move it into __replace_page() and fix the comment. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com> Cc: Anton Arapov <anton@redhat.com> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20120729182220.GA20322@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/events/uprobes.c | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 23c562b7fc2e..5db150b306d2 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -139,10 +139,15 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, struct mm_struct *mm = vma->vm_mm; spinlock_t *ptl; pte_t *ptep; + int err; + /* freeze PageSwapCache() for try_to_free_swap() below */ + lock_page(page); + + err = -EAGAIN; ptep = page_check_address(page, mm, addr, &ptl, 0); if (!ptep) - return -EAGAIN; + goto unlock; get_page(kpage); page_add_new_anon_rmap(kpage, vma, addr); @@ -162,7 +167,10 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, put_page(page); pte_unmap_unlock(ptep, ptl); - return 0; + err = 0; + unlock: + unlock_page(page); + return err; } /** @@ -216,15 +224,10 @@ retry: ret = -ENOMEM; new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr); if (!new_page) - goto put_out; + goto put_old; __SetPageUptodate(new_page); - /* - * lock page will serialize against do_wp_page()'s - * PageAnon() handling - */ - lock_page(old_page); /* copy the page now that we've got it stable */ vaddr_old = kmap_atomic(old_page); vaddr_new = kmap_atomic(new_page); @@ -237,15 +240,13 @@ retry: ret = anon_vma_prepare(vma); if (ret) - goto unlock_out; + goto put_new; ret = __replace_page(vma, vaddr, old_page, new_page); -unlock_out: - unlock_page(old_page); +put_new: page_cache_release(new_page); - -put_out: +put_old: put_page(old_page); if (unlikely(ret == -EAGAIN)) -- 2.20.1