linux-ext4 - Doubt about race condition between fallocate() and writeback path

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Message-ID: <CAD+278W-BG5tNPBJJ=gYwyygrotk+58-OCmv_LfsgHEwSAPEVw@mail.gmail.com>
Date: Tue, 25 Feb 2025 16:57:16 +0530
From: RSINGH <rsingh.ind.1272@...il.com>
To: linux-ext4@...r.kernel.org
Subject: Doubt about race condition between fallocate() and writeback path

Hi!

I had the following doubt related to interaction between fallocate(),
write() and writeback path
Can someone please provide insights?

In ext4_punch_hole(), writeout of dirty pages is done before acquiring
inode lock as shown below:

==========================================
/*
* Write out all dirty pages to avoid race conditions
* Then release them.
*/
if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
ret = filemap_write_and_wait_range(mapping, offset,
  offset + length - 1);
if (ret)
return ret;
}

inode_lock(inode);
==========================================

Isn't there a chance that after writing dirty pages and before
acquiring inode lock, more pages can get dirtied while writeback path
is also processing the dirty pages?

Regards,
RS