linux-kernel - Re: [PATCH] bcachefs: Fix deadlocks between fallocate and readahead

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Message-ID: <20250929075644.338686-1-kartikey406@gmail.com>
Date: Mon, 29 Sep 2025 13:26:43 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: kent.overstreet@...ux.dev
Cc: linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re:  [PATCH] bcachefs: Fix deadlocks between fallocate and readahead

I found that bchfs_fallocate() only evicts pagecache when FALLOC_FL_ZERO_RANGE is set:

if (mode & FALLOC_FL_ZERO_RANGE) {
    ret = bch2_truncate_folios(inode, offset, end);
    truncate_pagecache_range(&inode->v, offset, end - 1);
}

So basic fallocate (mode=0 or just KEEP_SIZE) doesn't evict pages and shouldn't need pagecache_block_get().

Should the fix be to only acquire pagecache_block_get() for modes that actually evict (ZERO_RANGE, PUNCH_HOLE, INSERT/COLLAPSE)?