From: Roman Pen Subject: [PATCH 0/3] ext4: fallocate insert/collapse range fixes Date: Mon, 2 Jan 2017 13:54:47 +0100 Message-ID: <20170102125450.22807-1-roman.penyaev@profitbricks.com> Cc: Roman Pen , Namjae Jeon , "Theodore Ts'o" , Andreas Dilger , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: unlisted-recipients:; (no To-header on input) Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Hi all. For couple of days I've played with inserting and collapsing range using fallocate and have found two nasty bugs: 1. On right shift (insert range) start block is not included in the range and hole appears at the wrong offset. The bug can be easily reproduced by the following test: ptr = malloc(4096); assert(ptr); fd = open("./ext4.file", O_CREAT | O_TRUNC | O_RDWR, 0600); assert(fd >= 0); rc = fallocate(fd, 0, 0, 8192); assert(rc == 0); for (i = 0; i < 2048; i++) *((unsigned short *)ptr + i) = 0xbeef; rc = pwrite(fd, ptr, 4096, 0); assert(rc == 4096); rc = pwrite(fd, ptr, 4096, 4096); assert(rc == 4096); for (block = 2; block < 1000; block++) { rc = fallocate(fd, FALLOC_FL_INSERT_RANGE, 4096, 4096); assert(rc == 0); for (i = 0; i < 2048; i++) *((unsigned short *)ptr + i) = block; rc = pwrite(fd, ptr, 4096, 4096); assert(rc == 4096); } After the test no zero blocks should appear (test always does pwrite() after fallocate), but zero blocks do exist: $ hexdump ./ext4.file | grep '0000 0000' This bug is targeted by the first patch in the set. 2. Inside ext4_ext_shift_extents() function ext4_find_extent() is called without EXT4_EX_NOCACHE flag, which should prevent cache population. This leads to outdated offsets in the extents tree and wrong data blocks, which can be observed doing read(). That is also quite well reproduced by the test above. This is fixed by the second patch. 3. Just a minor optimization: linear search of a extent inside a block is replaced by a binsearch. This is the third patch. Roman Pen (3): ext4: Include forgotten start block on fallocate insert range ext4: Do not populate extents tree with outdated offsets while shifting extents ext4: Find desired extent in ext4_ext_shift_extents() using binsearch fs/ext4/extents.c | 40 +++++++++++++++++++++++++++------------- 1 file changed, 27 insertions(+), 13 deletions(-) Signed-off-by: Roman Pen Cc: Namjae Jeon Cc: "Theodore Ts'o" Cc: Andreas Dilger Cc: linux-ext4@vger.kernel.org Cc: linux-kernel@vger.kernel.org -- 2.10.2