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Message-ID: <52b8bab4-6656-fe76-ed21-ee3c4682a5e3@huawei.com> Date: Sat, 25 Nov 2017 09:52:13 +0800 From: 郭雪楠 <guoxuenan@...wei.com> To: Michal Hocko <mhocko@...nel.org> CC: <akpm@...ux-foundation.org>, <minchan@...nel.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, <rppt@...ux.vnet.ibm.com>, <yi.zhang@...wei.com>, <miaoxie@...wei.com>, <aarcange@...hat.com>, <mgorman@...hsingularity.net>, <kirill.shutemov@...ux.intel.com>, <rientjes@...gle.com>, <khandual@...ux.vnet.ibm.com>, <riel@...hat.com>, <hillf.zj@...baba-inc.com>, <shli@...com> Subject: Re: [PATCH] mm,madvise: bugfix of madvise systemcall infinite loop under special circumstances. Yes , your modification is much better! thanks. 在 2017/11/24 21:08, Michal Hocko 写道: > On Fri 24-11-17 20:51:29, 郭雪楠 wrote: >> Sorry,I explained wrong before. But,I've tested using trinity in DAX >> mode,and I'am sure it has possibility of triggering an soft lockup. I have >> encountered the problem of endless loop here . >> >> I had a little problem here,I correct it . >> under Initial state : >> [ start = vam->vm_start < vam->vm_end < end ] >> >> When [start = vam->vm_start] the program enters for{;;} loop >> ,find_vma_prev() will set the pointer vma and the pointer prev (prev = >> vam->vm_prev ). Normally ,madvise_vma() will always move the pointer prev >> ,but when use DAX mode , it will never update . > [...] >> if (prev) // here prev not NULL,it will always enter this branch .. >> vma = prev->vm_next; >> else /* madvise_remove dropped mmap_sem */ >> vma = find_vma(current->mm, start); > > You are right! My fault, I managed to confuse myself in the code flow. > It really looks like this has been broken for more than 10 years since > fe77ba6f4f97 ("[PATCH] xip: madvice/fadvice: execute in place"). > > Maybe the following would be more readable and less error prone? > --- > diff --git a/mm/madvise.c b/mm/madvise.c > index 375cf32087e4..a631c414f915 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -276,30 +276,26 @@ static long madvise_willneed(struct vm_area_struct *vma, > { > struct file *file = vma->vm_file; > > + *prev = vma; > #ifdef CONFIG_SWAP > if (!file) { > - *prev = vma; > force_swapin_readahead(vma, start, end); > return 0; > } > > - if (shmem_mapping(file->f_mapping)) { > - *prev = vma; > + if (shmem_mapping(file->f_mapping)) > force_shm_swapin_readahead(vma, start, end, > file->f_mapping); > return 0; > - } > #else > if (!file) > return -EBADF; > #endif > > - if (IS_DAX(file_inode(file))) { > + if (IS_DAX(file_inode(file))) > /* no bad return value, but ignore advice */ > return 0; > - } > > - *prev = vma; > start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; > if (end > vma->vm_end) > end = vma->vm_end; >
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