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[PATCH] direct-io: don't introduce another read of inode->i_blkbits

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Commit 20ce44d545844 ("do_direct_IO: Use inode->i_blkbits to compute
block count to be cleaned") introduced a regression: if the block size
of the block device is changed while a direct I/O request is being
setup, it can result in a panic.  See commit ab73857e354ab ("direct-io:
don't read inode->i_blkbits multiple times") for the reasoning, and
commit b87570f5d3496 ("Fix a crash when block device is read and block
size is changed at the same time") for a more detailed problem
description and reproducer.

Fixes: 20ce44d545844
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

---
Chandan, can you please test this to ensure this still fixes your problem?

diff --git a/fs/direct-io.c b/fs/direct-io.c
index b20adf9..c87bae4 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -905,8 +905,8 @@ static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
 			struct buffer_head *map_bh)
 {
-	const unsigned i_blkbits = dio->inode->i_blkbits;
 	const unsigned blkbits = sdio->blkbits;
+	const unsigned i_blkbits = blkbits + sdio->blkfactor;
 	int ret = 0;
 
 	while (sdio->block_in_file < sdio->final_block_in_request) {

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Thread

[PATCH] do_direct_IO: Use inode->i_blkbits to compute block count to be cleaned Chandan Rajendra <chandan@linux.vnet.ibm.com> - 2017-01-08 15:50 +0100
  Re: [PATCH] do_direct_IO: Use inode->i_blkbits to compute block  count to be cleaned Christoph Hellwig <hch@infradead.org> - 2017-01-09 15:00 +0100
  Re: [PATCH] do_direct_IO: Use inode->i_blkbits to compute block count  to be cleaned Jens Axboe <axboe@kernel.dk> - 2017-01-09 16:40 +0100
  Re: [PATCH] do_direct_IO: Use inode->i_blkbits to compute block count to be cleaned Jeff Moyer <jmoyer@redhat.com> - 2017-01-09 17:10 +0100
  Re: [PATCH] do_direct_IO: Use inode->i_blkbits to compute block  count to be cleaned Jan Kara <jack@suse.cz> - 2017-01-09 21:30 +0100
  Re: [PATCH] direct-io: don't introduce another read of  inode->i_blkbits Jens Axboe <axboe@kernel.dk> - 2017-01-09 22:50 +0100
  [PATCH] direct-io: don't introduce another read of inode->i_blkbits Jeff Moyer <jmoyer@redhat.com> - 2017-01-09 22:50 +0100
    Re: [PATCH] direct-io: don't introduce another read of inode->i_blkbits Chandan Rajendra <chandan@linux.vnet.ibm.com> - 2017-01-10 06:30 +0100
      Re: [PATCH] direct-io: don't introduce another read of  inode->i_blkbits Jens Axboe <axboe@kernel.dk> - 2017-01-10 21:40 +0100

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