Messages in this thread | | | Date | Tue, 13 May 2003 15:49:29 -0700 | From | William Lee Irwin III <> | Subject | Re: Race between vmtruncate and mapped areas? |
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On Tue, May 13, 2003 at 05:26:24PM -0500, Dave McCracken wrote: > Hmm... Yep, it is. I did some more investigating. My initial scenario > required that the task mapping the page extend the file after the truncate, > which must be done via some kind of write(). The write() would trip over > i_sem and therefore hang waiting for vmtruncate() to complete. So I was > wrong about that one. > Hoever, vmtruncate() does get to truncate_complete_page() with a page > that's mapped... > After some though it occurred to me there is a simple alternative scenario > that's not protected. If a task is *already* in a page fault mapping the > page in, then vmtruncate() could call zap_page_range() before the page > fault completes. When the page fault does complete the page will be mapped > into the area previously cleared by vmtruncate(). > We could make vmtruncate() take mmap_sem for write, but that seems somewhat > drastic. Does anyone have any alternative ideas?
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.
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