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ext4: fix a potential fiemap/page fault deadlock w/ inline_data 

commit 2b08b1f12cd664dc7d5c84ead9ff25ae97ad5491 upstream.

The ext4_inline_data_fiemap() function calls fiemap_fill_next_extent()
while still holding the xattr semaphore.  This is not necessary and it
triggers a circular lockdep warning.  This is because
fiemap_fill_next_extent() could trigger a page fault when it writes
into page which triggers a page fault.  If that page is mmaped from
the inline file in question, this could very well result in a
deadlock.

This problem can be reproduced using generic/519 with a file system
configuration which has the inline_data feature enabled.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Theodore Ts'o 2018-12-25 00:56:33 -05:00 committed by syphyr
parent 076977825d
commit b8c60b0546
1 changed files with 3 additions and 3 deletions
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6
fs/ext4/inline.c
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@ -1864,12 +1864,12 @@ int ext4_inline_data_fiemap(struct inode *inode,
physical += (char *)ext4_raw_inode(&iloc) - iloc.bh->b_data;
physical += offsetof(struct ext4_inode, i_block);
if (physical)
error = fiemap_fill_next_extent(fieinfo, start, physical,
inline_len, flags);
brelse(iloc.bh);
out:
up_read(&EXT4_I(inode)->xattr_sem);
if (physical)
error = fiemap_fill_next_extent(fieinfo, start, physical,
inline_len, flags);
return (error < 0 ? error : 0);
}