Bug 70622 - fsync_inode_buffers is unreliable
fsync_inode_buffers is unreliable
Product: Red Hat Enterprise Linux 2.1
Classification: Red Hat
Component: kernel (Show other bugs)
i686 Linux
medium Severity medium
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Assigned To: Larry Woodman
Brian Brock
Depends On:
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Reported: 2002-08-02 17:45 EDT by Tim Wright
Modified: 2007-11-30 17:06 EST (History)
0 users

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Doc Type: Bug Fix
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Last Closed: 2005-04-04 14:17:44 EDT
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Description Tim Wright 2002-08-02 17:45:48 EDT
Description of Problem:
The routine fsync_inode_buffers() should write out the dirty buffers for the
specified inode, but there exists a scenario where it can return having failed
to do so:
bdflush() runs and gets its hands on a dirty buffer. It locks, cleans, and
submits it.  Before the I/O completes, commit_write() dirties it again.
Now fsync_inode_buffers() runs.  It sees the buffer as dirty, so it calls
ll_rw_block() on it, but its try lock fails, so it does nothing.
fsync_inode_buffers() later waits on the buffer.  Then the I/O finally
completes, and fsync_inode_buffers() returns.  That I/O was on a previous
version of the block -- the latest data have not necessarily reached the disk yet.

Version-Release number of selected component (if applicable):
2.4.9-e.3, e.5 and e.8

How Reproducible:

Steps to Reproduce:
1. This is a race condition. We encountered it in work on a shared/clustered
filesystem. Corruption occurred and the bug was found through inspection.

Actual Results:
Occasionally, not all buffers will be flushed when fsync_inode_buffers returns.
In a clustered filesystem, this can cause data corruption.

Expected Results:
All dirty buffers should have been written at least in the form they were at the
time of the call on return from fsync_inode_buffers.

Additional Information:
This causes data corruption for a shared/clustered filesytem which needs to use
clusterwide inode locks and expects fsync_inode_buffers() reliably write all the
dirty buffers.
Comment 1 Tim Wright 2002-09-23 16:59:58 EDT
FYI, the patch for this bug made it into 2.4.19.



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