On Wed, Jan 28, 2026 at 04:26:20PM +0100, Christoph Hellwig wrote:
> Currently all reads of the fsverity hashes is kicked off from the data
> I/O completion handler, leading to needlessly dependent I/O. This is
> worked around a bit by performing readahead on the level 0 nodes, but
> still fairly ineffective.
>
> Switch to a model where the ->read_folio and ->readahead methods instead
> kick off explicit readahead of the fsverity hashed so they are usually
> available at I/O completion time.
>
> For 64k sequential reads on my test VM this improves read performance
> from 2.4GB/s - 2.6GB/s to 3.5GB/s - 3.9GB/s. The improvements for
> random reads are likely to be even bigger.
>
> Signed-off-by: Christoph Hellwig <[email protected]>
> Acked-by: David Sterba <[email protected]> [btrfs]
Unfortunately, this patch causes recursive down_read() of
address_space::invalidate_lock. How was this meant to work?
[ 20.563185] ============================================
[ 20.564179] WARNING: possible recursive locking detected
[ 20.565170] 6.19.0-rc7-00041-g7bd72c6393ab #2 Not tainted
[ 20.566180] --------------------------------------------
[ 20.567169] cmp/2320 is trying to acquire lock:
[ 20.568019] ffff888108465030 (mapping.invalidate_lock#2){++++}-{4:4}, at:
page_cache_ra_unbounded+0x6f/0x280
[ 20.569828]
[ 20.569828] but task is already holding lock:
[ 20.570914] ffff888108465030 (mapping.invalidate_lock#2){++++}-{4:4}, at:
page_cache_ra_unbounded+0x6f/0x280
[ 20.572739]
[ 20.572739] other info that might help us debug this:
[ 20.573938] Possible unsafe locking scenario:
[ 20.573938]
[ 20.575042] CPU0
[ 20.575522] ----
[ 20.576003] lock(mapping.invalidate_lock#2);
[ 20.576849] lock(mapping.invalidate_lock#2);
[ 20.577698]
[ 20.577698] *** DEADLOCK ***
[ 20.577698]
[ 20.578795] May be due to missing lock nesting notation
[ 20.578795]
[ 20.580045] 1 lock held by cmp/2320:
[ 20.580726] #0: ffff888108465030 (mapping.invalidate_lock#2){++++}-{4:4},
at: page_cache_ra_unbounded+0x6f/0x20
[ 20.582596]
[ 20.582596] stack backtrace:
[ 20.583428] CPU: 0 UID: 0 PID: 2320 Comm: cmp Not tainted
6.19.0-rc7-00041-g7bd72c6393ab #2 PREEMPT(none)
[ 20.583433] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Arch
Linux 1.17.0-2-2 04/01/2014
[ 20.583435] Call Trace:
[ 20.583437] <TASK>
[ 20.583438] show_stack+0x48/0x60
[ 20.583446] dump_stack_lvl+0x75/0xb0
[ 20.583451] dump_stack+0x14/0x1a
[ 20.583452] print_deadlock_bug.cold+0xc0/0xca
[ 20.583457] validate_chain+0x4ca/0x970
[ 20.583463] __lock_acquire+0x587/0xc40
[ 20.583465] ? find_held_lock+0x31/0x90
[ 20.583470] lock_acquire.part.0+0xaf/0x230
[ 20.583472] ? page_cache_ra_unbounded+0x6f/0x280
[ 20.583474] ? debug_smp_processor_id+0x1b/0x30
[ 20.583481] lock_acquire+0x67/0x140
[ 20.583483] ? page_cache_ra_unbounded+0x6f/0x280
[ 20.583484] down_read+0x40/0x180
[ 20.583487] ? page_cache_ra_unbounded+0x6f/0x280
[ 20.583489] page_cache_ra_unbounded+0x6f/0x280
[ 20.583491] ? lock_acquire.part.0+0xaf/0x230
[ 20.583492] ? __this_cpu_preempt_check+0x17/0x20
[ 20.583495] generic_readahead_merkle_tree+0x133/0x140
[ 20.583501] ext4_readahead_merkle_tree+0x2a/0x30
[ 20.583507] fsverity_readahead+0x9d/0xc0
[ 20.583510] ext4_mpage_readpages+0x194/0x9b0
[ 20.583515] ? __lock_release.isra.0+0x5e/0x160
[ 20.583517] ext4_readahead+0x3a/0x40
[ 20.583521] read_pages+0x84/0x370
[ 20.583523] page_cache_ra_unbounded+0x16c/0x280
[ 20.583525] page_cache_ra_order+0x10c/0x170
[ 20.583527] page_cache_sync_ra+0x1a1/0x360
[ 20.583528] filemap_get_pages+0x141/0x4c0
[ 20.583532] ? __this_cpu_preempt_check+0x17/0x20
[ 20.583534] filemap_read+0x11f/0x540
[ 20.583536] ? __folio_batch_add_and_move+0x7c/0x330
[ 20.583539] ? __this_cpu_preempt_check+0x17/0x20
[ 20.583541] generic_file_read_iter+0xc1/0x110
[ 20.583543] ? do_pte_missing+0x13a/0x450
[ 20.583547] ext4_file_read_iter+0x51/0x17
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