Messages in this thread | | | Date | Wed, 31 Jan 2018 09:16:53 -0800 | Subject | mount stuck in infinite loop | From | (Francesco Ruggeri) |
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I had a few cases of mount getting stuck in an infinite loop. This happens when bdev->bd_inode->i_blkbits gets modified (for example by bd_set_size()) while *_fill_super() is between sb_min_blocksize() and sb_bread(), and the new value is inconsistent with the block size used in fill_super(). When this happens one can get into an infinite loop in __getblk_slow(), if grow_buffers() allocates/finds a page with a given index, but __find_get_block{_slow}() looks for (and does not find) a page with a different index.
I can reproduce it in 4.14.15 with the following script. I can also reproduce it in 4.9 and 3.18.
FILE=/tmp/fsfile MNT=/tmp/fsmnt LOOP=`losetup -f`
rm -rf $FILE $MNT
mkdir $MNT dd if=/dev/zero of=$FILE count=32 bs=1MiB losetup $LOOP $FILE mkfs -t ext4 $LOOP while true; do losetup -D $LOOP; losetup $LOOP $FILE; done \ 2>/dev/null >/dev/null & for ((i=0; i<100; i++)); do echo ================== $i; \ mount $LOOP $MNT; umount $MNT; done
The issue is that __find_get_block_slow() and grow_buffers() compute the page index in different ways. I am not sure what the correct solution should be here.
Thanks, Francesco Ruggeri
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