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Tue, 26 Mar 2024 17:33:06 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pankajraghav.com; s=MBO0001; t=1711470786; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3moU2wlvHsr8+p9ny8JT8xaCQs7lbw0goaeSoNHDbDc=; b=YG/rrmZS5RDXubydtX68X+RaWK/eokcLFx8xmRnde3361DFaGekau5YHR1Fi0jFuv1TU2K IxNElpVIEPCddV8SOUtdRHe8uazMsQLkiP3vP5EVBSOw4CH8hCGTaYOEuYe47ZBo67zIGC uId8BkyuZYZ79+v4C5NL2iViEaj9u7n2kzI+zDXf+jfPharGpymhh6LSXkI2DNYjKAwC70 0nzI2WZBoAFFNl+1A2WDU3Zx/59oXxsndeEV0UVfbTIhHkDhw/vGXfu+fCp9oGrIg//oDO R7v6sZcSaWxX+Q9Bc/h7jbAIfM85ToFgR8x+30XVQiDhJPSgBehcvkYfhcR2Pg== Message-ID: Date: Tue, 26 Mar 2024 17:33:00 +0100 MIME-Version: 1.0 Subject: Re: [PATCH v3 07/11] mm: do not split a folio if it has minimum folio order requirement Content-Language: en-US To: Zi Yan Cc: Matthew Wilcox , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, gost.dev@samsung.com, chandan.babu@oracle.com, hare@suse.de, mcgrof@kernel.org, djwong@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@fromorbit.com, akpm@linux-foundation.org, Pankaj Raghav References: <20240313170253.2324812-1-kernel@pankajraghav.com> <20240313170253.2324812-8-kernel@pankajraghav.com> From: Pankaj Raghav In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9EAC5C000F X-Stat-Signature: w7i5du4dapfqcwmembh1odq9q8aap3pp X-HE-Tag: 1711470791-172897 X-HE-Meta: U2FsdGVkX18SybEOgaGnn8lvQG4g7qKOsUjzsKEdM4FFQjwe36yxrtItvdI27V/pjueq3p7UBpqLE0oOv2rCiM4iOp4eCg/Ar59t2NJtoITMrbWdgbD88xI111eqwHiqBmkmNK8gJ1WvjcMTHNBQxs9T1DM0GX/E2S0sNZr2KPiGRkiQpafKDD+hXgzzJIKZcCDAOEGMZNEPfPLZmmjlLr5mdFf/+VnUal1w6JXQBHh+JczcFfdPFDQ+/NTjD7k/gbCfoCoQvbNT9YsTFezDE23wAz0WSNKZOdjhYO7MwJ9Eca1DCVjgSysyIxp/G5boHNprP/lUwn6iNYxwZasJ6FwDjeHexCvPGBbtxoKjN48UjGRNGW2kBcMbyHzIpCmcDgTXsYwvq2a/OxjotQQzZGmgBbAbWHbxDj6+UuA3BCExg62s88u9NTILy+kSsbWuXbBB9/R3sdeJqtNmWdGtmr8iymQKByTOX3LqD368Gr1kb9uc+bIhlbyYoGU3Rk2hQGcbyyjBxLemQ7E2S0fzyiRC1tuCOE96rjsNNfbUyKekZvpGT2TrE1D/aNZ3zAlWyvR0zK+oneUH09wIhigUDJe8POhmMzrEXP/nJCEvDGP+EzDSEnIebr7C2yMWkdX91O563sXMZGjYT9a0M8u3AOeBf5i/RlHmiwop+dDtbaHP/npGPbejdGhvyxA1yDbl6I5Iy62W3GP351O7WrC30xGhj/Ine4whoKGnDCfJTJxFzELz80Guyj8DRcLhxOwaB2MzSUIc3qP0lerdz8e9VdiB0PlElrjtArqYgzCxKBmuNt49BCEs3cmzYqLm7uRHDYwXbvzv6FEX7z2L1kHMhFO5oLVB84x0ofymMR9i3ripSs/aaxqn2BD5T2iK1fExv+qNvfOYAHZdeUdTnKMUz4f7YDb/nwk3As+1G+DDeBQWKCoAL0M5bAD5dETC7cttPKbl746/6/tLfcCLKhu EMvGsAKR czUj78hJA2ZAW2wqUFeLZu0i1GWgdzxYvL5NFccuwSptaTg7ehDhZmTtB5szvH0Hj06jJKMxN4AlFc+4WteoRRCBf/vmSCs2/VFciXtFPpKBDsulKUOX5IhRN74jsRQ+37a/+Dox+XgHdMou1Z9GO+H/tsSwdOx/Ip189UlZkqwitss8sQtkP75XMU6laq2EhaSX4bH9ZmGfMJN3YPQ2uDg8GKw/OVaGzT+ickRv4lcbRlAc38bqdA4fySHNIxnZfRXdHlH2xqBURZ4K8tIFuReNE1EgcjyertMYhVEGJZmNzZ+TLXH1c9KGD3kbNNf1up0p42/oaQTD7DVA8jiL0mARxFQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 26/03/2024 17:23, Zi Yan wrote: > On 26 Mar 2024, at 12:10, Pankaj Raghav (Samsung) wrote: > >> On Mon, Mar 25, 2024 at 07:06:04PM +0000, Matthew Wilcox wrote: >>> On Wed, Mar 13, 2024 at 06:02:49PM +0100, Pankaj Raghav (Samsung) wrote: >>>> From: Pankaj Raghav >>>> >>>> As we don't have a way to split a folio to a any given lower folio >>>> order yet, avoid splitting the folio in split_huge_page_to_list() if it >>>> has a minimum folio order requirement. >>> >>> FYI, Zi Yan's patch to do that is now in Andrew's tree. >>> c010d47f107f609b9f4d6a103b6dfc53889049e9 in current linux-next (dated >>> Feb 26) >> >> Yes, I started playing with the patches but I am getting a race condition >> resulting in a null-ptr-deref for which I don't have a good answer for >> yet. >> >> @zi yan Did you encounter any issue like this when you were testing? >> >> I did the following change (just a prototype) instead of this patch: >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 9859aa4f7553..63ee7b6ed03d 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3041,6 +3041,10 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >> { >> struct folio *folio = page_folio(page); >> struct deferred_split *ds_queue = get_deferred_split_queue(folio); >> + unsigned int mapping_min_order = mapping_min_folio_order(folio->mapping); > > I am not sure if this is right. Since folio can be anonymous and folio->mapping > does not point to struct address_space. > >> + >> + if (!folio_test_anon(folio)) Hmm, but I update the new_order only if it is not anonymous. Do you think it is still wrong? >> + new_order = max_t(unsigned int, mapping_min_order, new_order); >> /* reset xarray order to new order after split */ >> XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order); >> struct anon_vma *anon_vma = NULL; >> @@ -3117,6 +3121,8 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >> goto out; >> } >> >> + // XXX: Remove it later >> + VM_WARN_ON_FOLIO((new_order < mapping_min_order), folio); >> gfp = current_gfp_context(mapping_gfp_mask(mapping) & >> GFP_RECLAIM_MASK); >> >> I am getting a random null-ptr deref when I run generic/176 multiple >> times with different blksizes. I still don't have a minimal reproducer >> for this issue. Race condition during writeback: >> >> filemap_get_folios_tag+0x171/0x5c0: >> arch_atomic_read at arch/x86/include/asm/atomic.h:23 >> (inlined by) raw_atomic_read at include/linux/atomic/atomic-arch-fallback.h:457 >> (inlined by) raw_atomic_fetch_add_unless at include/linux/atomic/atomic-arch-fallback.h:2426 >> (inlined by) raw_atomic_add_unless at include/linux/atomic/atomic-arch-fallback.h:2456 >> (inlined by) atomic_add_unless at include/linux/atomic/atomic-instrumented.h:1518 >> (inlined by) page_ref_add_unless at include/linux/page_ref.h:238 >> (inlined by) folio_ref_add_unless at include/linux/page_ref.h:247 >> (inlined by) folio_ref_try_add_rcu at include/linux/page_ref.h:280 >> (inlined by) folio_try_get_rcu at include/linux/page_ref.h:313 >> (inlined by) find_get_entry at mm/filemap.c:1984 >> (inlined by) filemap_get_folios_tag at mm/filemap.c:2222 >> >> >> >> [ 537.863105] ================================================================== >> [ 537.863968] BUG: KASAN: null-ptr-deref in filemap_get_folios_tag+0x171/0x5c0 >> [ 537.864581] Write of size 4 at addr 0000000000000036 by task kworker/u32:5/366 >> [ 537.865123] >> [ 537.865293] CPU: 6 PID: 366 Comm: kworker/u32:5 Not tainted 6.8.0-11739-g7d0c6e7b5a7d-dirty #795 >> [ 537.867201] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 >> [ 537.868444] Workqueue: writeback wb_workfn (flush-254:32) >> [ 537.869055] Call Trace: >> [ 537.869341] >> [ 537.869569] dump_stack_lvl+0x4f/0x70 >> [ 537.869938] kasan_report+0xbd/0xf0 >> [ 537.870293] ? filemap_get_folios_tag+0x171/0x5c0 >> [ 537.870767] ? filemap_get_folios_tag+0x171/0x5c0 >> [ 537.871578] kasan_check_range+0x101/0x1b0 >> [ 537.871893] filemap_get_folios_tag+0x171/0x5c0 >> [ 537.872269] ? __pfx_filemap_get_folios_tag+0x10/0x10 >> [ 537.872857] ? __pfx___submit_bio+0x10/0x10 >> [ 537.873326] ? mlock_drain_local+0x234/0x3f0 >> [ 537.873938] writeback_iter+0x59a/0xe00 >> [ 537.874477] ? __pfx_iomap_do_writepage+0x10/0x10 >> [ 537.874969] write_cache_pages+0x7f/0x100 >> [ 537.875396] ? __pfx_write_cache_pages+0x10/0x10 >> [ 537.875892] ? do_raw_spin_lock+0x12d/0x270 >> [ 537.876345] ? __pfx_do_raw_spin_lock+0x10/0x10 >> [ 537.876804] iomap_writepages+0x88/0xf0 >> [ 537.877186] xfs_vm_writepages+0x120/0x190 >> [ 537.877705] ? __pfx_xfs_vm_writepages+0x10/0x10 >> [ 537.878161] ? lock_release+0x36f/0x670 >> [ 537.878521] ? __wb_calc_thresh+0xe5/0x3b0 >> [ 537.878892] ? __pfx_lock_release+0x10/0x10 >> [ 537.879308] do_writepages+0x170/0x7a0 >> [ 537.879676] ? __pfx_do_writepages+0x10/0x10 >> [ 537.880182] ? writeback_sb_inodes+0x312/0xe40 >> [ 537.880689] ? reacquire_held_locks+0x1f1/0x4a0 >> [ 537.881193] ? writeback_sb_inodes+0x312/0xe40 >> [ 537.881665] ? find_held_lock+0x2d/0x110 >> [ 537.882104] ? lock_release+0x36f/0x670 >> [ 537.883344] ? wbc_attach_and_unlock_inode+0x3b8/0x710 >> [ 537.883853] ? __pfx_lock_release+0x10/0x10 >> [ 537.884229] ? __pfx_lock_release+0x10/0x10 >> [ 537.884604] ? lock_acquire+0x138/0x2f0 >> [ 537.884952] __writeback_single_inode+0xd4/0xa60 >> [ 537.885369] writeback_sb_inodes+0x4cf/0xe40 >> [ 537.885760] ? __pfx_writeback_sb_inodes+0x10/0x10 >> [ 537.886208] ? __pfx_move_expired_inodes+0x10/0x10 >> [ 537.886640] __writeback_inodes_wb+0xb4/0x200 >> [ 537.887037] wb_writeback+0x55b/0x7c0 >> [ 537.887372] ? __pfx_wb_writeback+0x10/0x10 >> [ 537.887750] ? lock_acquire+0x138/0x2f0 >> [ 537.888094] ? __pfx_register_lock_class+0x10/0x10 >> [ 537.888521] wb_workfn+0x648/0xbb0 >> [ 537.888835] ? __pfx_wb_workfn+0x10/0x10 >> [ 537.889192] ? lock_acquire+0x128/0x2f0 >> [ 537.889539] ? lock_acquire+0x138/0x2f0 >> [ 537.889890] process_one_work+0x7ff/0x1710 >> [ 537.890272] ? __pfx_process_one_work+0x10/0x10 >> [ 537.890685] ? assign_work+0x16c/0x240 >> [ 537.891026] worker_thread+0x6e8/0x12b0 >> [ 537.891381] ? __pfx_worker_thread+0x10/0x10 >> [ 537.891768] kthread+0x2ad/0x380 >> [ 537.892064] ? __pfx_kthread+0x10/0x10 >> [ 537.892403] ret_from_fork+0x2d/0x70 >> [ 537.892728] ? __pfx_kthread+0x10/0x10 >> [ 537.893068] ret_from_fork_asm+0x1a/0x30 >> [ 537.893434] > > > -- > Best Regards, > Yan, Zi