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Date: Mon, 20 Jan 2014 15:20:05 +0530 From: Sandeep Joshi <sanjos100@...il.com> To: linux-kernel@...r.kernel.org Subject: sigbus on memcpy despite calling mincore Hi folks I have a program which is trying to read a page from the page cache for a certain file it calls mmap (PROT_NONE, MAP_SHARED |MAP_LOCKED). Then it calls mincore to check if the page is in memory If it does exist, it remaps the same offset using mmap(PROT_READ, MAP_SHARED|MAP_LOCKED) After this, it is tries to do a read (memcpy) from the returned address of the second mmap. Unfortunately, I am getting a SIGBUS in cases where there is another thread in the same process trying to write to the same file (though not at the same offset) when I look in /proc/<pid>/smaps, I see that the mapped address has RSS=0 (not in memory) and LOCKED=0 (not locked) which is strange since I have locked the page and called mincore on it. I added checking for the filesize (fstat) before the first mmap but still get a SIGBUS. I also changed the second and first mmaps to do MAP_PRIVATE hoping it would give a private copy of the page but that didnt help either. Is there some race condition which resets the vma_flags when another thread in the same process is writing to the same file offset being read ? thanks -Sandeep -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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