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