Date: Tue, 29 Sep 1998 11:14:03 -0700 (PDT) From: Matthew Dillon <dillon@backplane.com> To: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: A second mmap file corruption issue Message-ID: <199809291814.LAA20823@apollo.backplane.com>
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I've verified that the *other* mmap file corruption issue that Terry brought up is real. Here's what happened to me: -stable system news1.best.com All of diablo's mmap's are read-only shared. Diablo is operating fine, no problems. I kill Diablo and restart it. Suddenly, an mmap'd portion of diablo's history file is corrupted, containing a portion of some other file. Diablo shares pages and mmap's up the wazoo. What I believe happened was that all the page references in the mmap were hiding a wiring count failure in the bp code. When I exited diablo, I believe that a bp wound up with b_pages[] pointing to pages that were no longer wired and then the pages got reused. This is conjecture. I would like someone to look at the following code, though: (1) around line 659 of kern/vfs_bio.c, in brelse(). I think the page needs to be wired !!!!!!! Won't the wire count get corrupted when the bp is released and the page isn't wired ? if (m == bogus_page) { m = vm_page_lookup(obj, poff + j); ... bp->b_pages[j] = m; } (2) around line 1969 of kern/vfs_bio.c, in biodone. I think this page needs to be wired as well. if (m == bogus_page) { bogusflag = 1; m = vm_page_lookup(obj, OFF_TO_IDX(foff)); ... bp->b_pages[i] = m; pmap_qenter(trunc_page(bp->b_data), bp->b_pages, bp->b_npages); } (3) Could someone also check vfs_busy_pages() and vfs_unbusy_pages() ? busy_pages removes pages from the bp without unwiring them, presumably because unbusy_pages adds them back without wiring them. That seems rather fragile to me but I *think* the code is doing the right thing as long as all vfs_busy_pages() calls are matched by vfs_unbusy_pages() calls. -Matt Matthew Dillon Engineering, HiWay Technologies, Inc. & BEST Internet Communications & God knows what else. <dillon@backplane.com> (Please include original email in any response)
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