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SubjectRe: [PATCH 1/1]ext4: Fix WARN_ON_ONCE when marking buffer dirty
On Thu, Jun 30, 2016 at 02:12:30PM +0300, Pranay Kr. Srivastava wrote:
> Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>

The description for why the change is being made should go in the
commit. (No need to put the description in a separate cover letter.)
I ended up rewriting the commit description as follows, to make it
much more understandable:

ext4: Fix WARN_ON_ONCE in ext4_commit_super()

If there are racing calls to ext4_commit_super() it's possible for
another writeback of the superblock to result in the buffer being
marked with an error after we check if the buffer is marked as
having a write error and the buffer up-to-date flag is set again.
If that happens mark_buffer_dirty() can end up throwing a
WARN_ON_ONCE.

Fix this by moving this check to write before we call
write_buffer_dirty(), and keeping the buffer locked during this
whole sequence.

Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Note that the one-line summary needs to carry as much information as
possible so someone who is scanning the commits using git log
--oneline has a chance of understanding it. This means the high-level
*why* of the commit, not a summary of what the changes in the C code.
Also note the increased context of when the misbehaviour could occur
in the commit description, which was missing in the cover letter.

When I'm processing patches, if I'm in a hurry, patches that require
extra work or which aren't Obviously Right, sometimes get deferred by
a few days. This patch fell in that category.

Adding to the commit descrtipion additional context and/or
instructions for how to reproduce the problem you are trying to
remediate will often make life much easier for me, and accelerate how
quickly I'll get to your patch.

Cheers,

- Ted

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