On 2019/01/03 2:26, Jan Kara wrote: > On Thu 03-01-19 01:07:25, Tetsuo Handa wrote: >> On 2019/01/02 23:40, Jan Kara wrote: >>> I had a look into this and the only good explanation for this I have is >>> that sb->s_blocksize is different from (1 << sb->s_bdev->bd_inode->i_blkbits). >>> If that would happen, we'd get exactly the behavior syzkaller observes >>> because grow_buffers() would populate different page than >>> __find_get_block() then looks up. >>> >>> However I don't see how that's possible since the filesystem has the block >>> device open exclusively and blkdev_bszset() makes sure we also have >>> exclusive access to the block device before changing the block device size. >>> So changing block device block size after filesystem gets access to the >>> device should be impossible. >>> >>> Anyway, could you perhaps add to your debug patch a dump of 'size' passed >>> to __getblk_slow() and bdev->bd_inode->i_blkbits? That should tell us >>> whether my theory is right or not. Thanks! >>> Got two reports. 'size' is 512 while bdev->bd_inode->i_blkbits is 12. https://syzkaller.appspot.com/text?tag=CrashLog&x=1237c3ab400000 [ 385.723941][ T439] kworker/u4:3(439): getblk(): executed=9 bh_count=0 bh_state=0 bdev_super_blocksize=512 size=512 bdev_super_blocksize_bits=9 bdev_inode_blkbits=12 (...snipped...) [ 568.159544][ T439] kworker/u4:3(439): getblk(): executed=9 bh_count=0 bh_state=0 bdev_super_blocksize=512 size=512 bdev_super_blocksize_bits=9 bdev_inode_blkbits=12 https://syzkaller.appspot.com/text?tag=CrashLog&x=143383d7400000 [ 1355.681513][ T6893] syz-executor0(6893): getblk(): executed=9 bh_count=0 bh_state=0 bdev_super_blocksize=512 size=512 bdev_super_blocksize_bits=9 bdev_inode_blkbits=12 [ 1358.274585][T15649] kworker/u4:17(15649): getblk(): executed=9 bh_count=0 bh_state=0 bdev_super_blocksize=512 size=512 bdev_super_blocksize_bits=9 bdev_inode_blkbits=12 (...snipped...) [ 1455.341572][ T6893] syz-executor0(6893): getblk(): executed=9 bh_count=0 bh_state=0 bdev_super_blocksize=512 size=512 bdev_super_blocksize_bits=9 bdev_inode_blkbits=12 [ 1455.541457][T15649] kworker/u4:17(15649): getblk(): executed=9 bh_count=0 bh_state=0 bdev_super_blocksize=512 size=512 bdev_super_blocksize_bits=9 bdev_inode_blkbits=12 >> >> OK. Andrew, will you add (or fold into) this change? >> >> From e6f334380ad2c87457bfc2a4058316c47f75824a Mon Sep 17 00:00:00 2001 >> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> >> Date: Thu, 3 Jan 2019 01:03:35 +0900 >> Subject: [PATCH] fs/buffer.c: dump more info for __getblk_gfp() stall problem >> >> We need to dump more variables on top of >> "fs/buffer.c: add debug print for __getblk_gfp() stall problem". >> >> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> >> Cc: Jan Kara <jack@xxxxxxx> >> --- >> fs/buffer.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/fs/buffer.c b/fs/buffer.c >> index 580fda0..a50acac 100644 >> --- a/fs/buffer.c >> +++ b/fs/buffer.c >> @@ -1066,9 +1066,14 @@ static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size) >> #ifdef CONFIG_DEBUG_AID_FOR_SYZBOT >> if (!time_after(jiffies, current->getblk_stamp + 3 * HZ)) >> continue; >> - printk(KERN_ERR "%s(%u): getblk(): executed=%x bh_count=%d bh_state=%lx\n", >> + printk(KERN_ERR "%s(%u): getblk(): executed=%x bh_count=%d bh_state=%lx " >> + "bdev_super_blocksize=%lu size=%u " >> + "bdev_super_blocksize_bits=%u bdev_inode_blkbits=%u\n", >> current->comm, current->pid, current->getblk_executed, >> - current->getblk_bh_count, current->getblk_bh_state); >> + current->getblk_bh_count, current->getblk_bh_state, >> + bdev->bd_super->s_blocksize, size, >> + bdev->bd_super->s_blocksize_bits, >> + bdev->bd_inode->i_blkbits); > > Well, bd_super may be NULL if there's no filesystem mounted so it would be > safer to check for this rather than blindly dereferencing it... Otherwise > the change looks good to me. > > Honza >
