From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 13 May 2003 16:11:39 -0700 From: William Lee Irwin III Subject: Re: Race between vmtruncate and mapped areas? Message-ID: <20030513231139.GZ8978@holomorphy.com> References: <154080000.1052858685@baldur.austin.ibm.com> <3EC15C6D.1040403@kolumbus.fi> <199610000.1052864784@baldur.austin.ibm.com> <20030513224929.GX8978@holomorphy.com> <220550000.1052866808@baldur.austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <220550000.1052866808@baldur.austin.ibm.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Dave McCracken Cc: Mika Penttil? , Linux Memory Management , Linux Kernel List-ID: On Tuesday, May 13, 2003 15:49:29 -0700 William Lee Irwin III wrote: >> That doesn't sound like it's going to help, there isn't a unique >> mmap_sem to be taken and so we just get caught between acquisitions >> with the same problem. On Tue, May 13, 2003 at 06:00:08PM -0500, Dave McCracken wrote: > Actually it does fix it. I added code in vmtruncate_list() to do a > down_write(&vma->vm_mm->mmap_sem) around the zap_page_range(), and the > problem went away. It serializes against any outstanding page faults on a > particular page table. New faults will see that the page is no longer in > the file and fail with SIGBUS. Andrew's test case stopped failing. > I've attached the patch so you can see what I did. > Can anyone think of any gotchas to this solution? Okay, what's stopping filemap_nopage() from fetching the page from pagecache after one of the mm->mmap_sem's is dropped but before truncate_inode_pages() removes the page? The fault path is only locked out for one mm during one part of the operation. I can see taking ->i_sem in do_no_page() fixing it, but not ->mmap_sem in vmtruncate() (but of course that's _far_ too heavy-handed to merge at all). -- wli -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org