From: Hin-Tak Leung <htl10@xxxxxxxxxxxxxxxxxxxxx> Subject: hfs,hfsplus: cache pages correctly between bnode_create and bnode_free Pages looked up by __hfs_bnode_create() (called by hfs_bnode_create() and hfs_bnode_find() for finding or creating pages corresponding to an inode) are immediately kmap()'ed and used (both read and write) and kunmap()'ed, and should not be page_cache_release()'ed until hfs_bnode_free(). This patch fixes a problem I first saw in July 2012: merely running "du" on a large hfsplus-mounted directory a few times on a reasonably loaded system would get the hfsplus driver all confused and complaining about B-tree inconsistencies, and generates a "BUG: Bad page state". Most recently, I can generate this problem on up-to-date Fedora 22 with shipped kernel 4.0.5, by running "du /" (="/" + "/home" + "/mnt" + other smaller mounts) and "du /mnt" simultaneously on two windows, where /mnt is a lightly-used QEMU VM image of the full Mac OS X 10.9: $ df -i / /home /mnt Filesystem Inodes IUsed IFree IUse% Mounted on /dev/mapper/fedora-root 3276800 551665 2725135 17% / /dev/mapper/fedora-home 52879360 716221 52163139 2% /home /dev/nbd0p2 4294967295 1387818 4293579477 1% /mnt After applying the patch, I was able to run "du /" (60+ times) and "du /mnt" (150+ times) continuously and simultaneously for 6+ hours. There are many reports of the hfsplus driver getting confused under load and generating "BUG: Bad page state" or other similar issues over the years. [1] The unpatched code [2] has always been wrong since it entered the kernel tree. The only reason why it gets away with it is that the kmap/memcpy/kunmap follow very quickly after the page_cache_release() so the kernel has not had a chance to reuse the memory for something else, most of the time. The current RW driver appears to have followed the design and development of the earlier read-only hfsplus driver [3], where-by version 0.1 (Dec 2001) had a B-tree node-centric approach to read_cache_page()/page_cache_release() per bnode_get()/bnode_put(), migrating towards version 0.2 (June 2002) of caching and releasing pages per inode extents. When the current RW code first entered the kernel [2] in 2005, there was an REF_PAGES conditional (and "//" commented out code) to switch between B-node centric paging to inode-centric paging. There was a mistake with the direction of one of the REF_PAGES conditionals in __hfs_bnode_create(). In a subsequent "remove debug code" commit [4], the read_cache_page()/page_cache_release() per bnode_get()/bnode_put() were removed, but a page_cache_release() was mistakenly left in (propagating the "REF_PAGES <-> !REF_PAGE" mistake), and the commented-out page_cache_release() in bnode_release() (which should be spanned by !REF_PAGES) was never enabled. References: [1]: Michael Fox, Apr 2013 http://www.spinics.net/lists/linux-fsdevel/msg63807.html ("hfsplus volume suddenly inaccessable after 'hfs: recoff %d too large'") Sasha Levin, Feb 2015 http://lkml.org/lkml/2015/2/20/85 ("use after free") https://bugs.launchpad.net/ubuntu/+source/linux/+bug/740814 https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1027887 https://bugzilla.kernel.org/show_bug.cgi?id=42342 https://bugzilla.kernel.org/show_bug.cgi?id=63841 https://bugzilla.kernel.org/show_bug.cgi?id=78761 [2]: http://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/\ fs/hfs/bnode.c?id=d1081202f1d0ee35ab0beb490da4b65d4bc763db commit d1081202f1d0ee35ab0beb490da4b65d4bc763db Author: Andrew Morton <akpm@xxxxxxxx> Date: Wed Feb 25 16:17:36 2004 -0800 [PATCH] HFS rewrite http://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/\ fs/hfsplus/bnode.c?id=91556682e0bf004d98a529bf829d339abb98bbbd commit 91556682e0bf004d98a529bf829d339abb98bbbd Author: Andrew Morton <akpm@xxxxxxxx> Date: Wed Feb 25 16:17:48 2004 -0800 [PATCH] HFS+ support [3]: http://sourceforge.net/projects/linux-hfsplus/ http://sourceforge.net/projects/linux-hfsplus/files/Linux%202.4.x%20patch/hfsplus%200.1/ http://sourceforge.net/projects/linux-hfsplus/files/Linux%202.4.x%20patch/hfsplus%200.2/ http://linux-hfsplus.cvs.sourceforge.net/viewvc/linux-hfsplus/linux/\ fs/hfsplus/bnode.c?r1=1.4&r2=1.5 Date: Thu Jun 6 09:45:14 2002 +0000 Use buffer cache instead of page cache in bnode.c. Cache inode extents. [4]: http://git.kernel.org/cgit/linux/kernel/git/\ stable/linux-stable.git/commit/?id=a5e3985fa014029eb6795664c704953720cc7f7d commit a5e3985fa014029eb6795664c704953720cc7f7d Author: Roman Zippel <zippel@xxxxxxxxxxxxxx> Date: Tue Sep 6 15:18:47 2005 -0700 [PATCH] hfs: remove debug code Signed-off-by: Hin-Tak Leung <htl10@xxxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sergei Antonov <saproj@xxxxxxxxx> Reviewed-by: Anton Altaparmakov <anton@xxxxxxxxxx> Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: Vyacheslav Dubeyko <slava@xxxxxxxxxxx> Cc: Sougata Santra <sougata@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/hfs/bnode.c | 9 ++++----- fs/hfsplus/bnode.c | 3 --- 2 files changed, 4 insertions(+), 8 deletions(-) diff -puN fs/hfs/bnode.c~hfshfsplus-cache-pages-correctly-between-bnode_create-and-bnode_free fs/hfs/bnode.c --- a/fs/hfs/bnode.c~hfshfsplus-cache-pages-correctly-between-bnode_create-and-bnode_free +++ a/fs/hfs/bnode.c @@ -288,7 +288,6 @@ static struct hfs_bnode *__hfs_bnode_cre page_cache_release(page); goto fail; } - page_cache_release(page); node->page[i] = page; } @@ -398,11 +397,11 @@ node_error: void hfs_bnode_free(struct hfs_bnode *node) { - //int i; + int i; - //for (i = 0; i < node->tree->pages_per_bnode; i++) - // if (node->page[i]) - // page_cache_release(node->page[i]); + for (i = 0; i < node->tree->pages_per_bnode; i++) + if (node->page[i]) + page_cache_release(node->page[i]); kfree(node); } diff -puN fs/hfsplus/bnode.c~hfshfsplus-cache-pages-correctly-between-bnode_create-and-bnode_free fs/hfsplus/bnode.c --- a/fs/hfsplus/bnode.c~hfshfsplus-cache-pages-correctly-between-bnode_create-and-bnode_free +++ a/fs/hfsplus/bnode.c @@ -454,7 +454,6 @@ static struct hfs_bnode *__hfs_bnode_cre page_cache_release(page); goto fail; } - page_cache_release(page); node->page[i] = page; } @@ -566,13 +565,11 @@ node_error: void hfs_bnode_free(struct hfs_bnode *node) { -#if 0 int i; for (i = 0; i < node->tree->pages_per_bnode; i++) if (node->page[i]) page_cache_release(node->page[i]); -#endif kfree(node); } _ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html