From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 38529154C17; Wed, 21 May 2025 22:09:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747865392; cv=none; b=h0YhcB2UE0bWRA7UoKivsRviJc2im6Ika/90+hMTKCcg1iXYiO+7UvfmQ9Njdpaodpfhwrgul/+BJZJWPbVoC7rEVE8oKrkkbxkI6LABAP5j43MPc90+ywAkM9dnGmC/3nP6zBrAiLqfwyzS6dxy0S4fMydDfCr1BmUYtN0BoV4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747865392; c=relaxed/simple; bh=gyJtVqSWzcUESI8kIeu1YEyvysWQrxilFbUyVe6f1RI=; h=Date:To:From:Subject:Message-Id; b=RALo9Z4Y+heghF2VIehag9cfNu7uRKdVOB1+pS0KrJGZV7dWfGTly829F7PRwvFbGA3WOK7bLOUG0vRMnWuBRc8PY5ap8uvZlWhVN2Xt85XKp7OrjUqSjIGFJag0MxlNNV1Mu+GLIZPhKxIzM1r/E+Fhn/h4OFyqvu8/nwfoZpU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=Tvst8qxL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="Tvst8qxL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 979ACC4CEE4; Wed, 21 May 2025 22:09:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1747865391; bh=gyJtVqSWzcUESI8kIeu1YEyvysWQrxilFbUyVe6f1RI=; h=Date:To:From:Subject:From; b=Tvst8qxLaMjPjppgecmhWk/RLmoFHs3dF/7Y2Pi11BYm3WHb3Z3eEgF8DYLpiLIZu llB8q7AfQJj3B+7uFYg0VYf3SmK1KoAJMVa//Z146+hh/ouZuVdSS52sf+tDiuwlbS CJAi2zaVPZdr2j5PjMiAFw/EY4P/AgGILccAOGv8= Date: Wed, 21 May 2025 15:09:50 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,revest@google.com,osalvador@suse.de,muchun.song@linux.dev,hughd@google.com,gshan@redhat.com,byungchul@sk.com,gavinguo@igalia.com,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-hugetlb-fix-a-deadlock-with-pagecache_folio-and-hugetlb_fault_mutex_table.patch removed from -mm tree Message-Id: <20250521220951.979ACC4CEE4@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/hugetlb: fix a deadlock with pagecache_folio and hugetlb_fault_mutex_table has been removed from the -mm tree. Its filename was mm-hugetlb-fix-a-deadlock-with-pagecache_folio-and-hugetlb_fault_mutex_table.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: Gavin Guo Subject: mm/hugetlb: fix a deadlock with pagecache_folio and hugetlb_fault_mutex_table Date: Tue, 13 May 2025 17:34:48 +0800 Fix a deadlock which can be triggered by an internal syzkaller [1] reproducer and captured by bpftrace script [2] and its log [3] in this scenario: Process 1 Process 2 --- --- hugetlb_fault mutex_lock(B) // take B filemap_lock_hugetlb_folio filemap_lock_folio __filemap_get_folio folio_lock(A) // take A hugetlb_wp mutex_unlock(B) // release B ... hugetlb_fault ... mutex_lock(B) // take B filemap_lock_hugetlb_folio filemap_lock_folio __filemap_get_folio folio_lock(A) // blocked unmap_ref_private ... mutex_lock(B) // retake and blocked This is a ABBA deadlock involving two locks: - Lock A: pagecache_folio lock - Lock B: hugetlb_fault_mutex_table lock The deadlock occurs between two processes as follows: 1. The first process (let's call it Process 1) is handling a copy-on-write (COW) operation on a hugepage via hugetlb_wp. Due to insufficient reserved hugetlb pages, Process 1, owner of the reserved hugetlb page, attempts to unmap a hugepage owned by another process (non-owner) to satisfy the reservation. Before unmapping, Process 1 acquires lock B (hugetlb_fault_mutex_table lock) and then lock A (pagecache_folio lock). To proceed with the unmap, it releases Lock B but retains Lock A. After the unmap, Process 1 tries to reacquire Lock B. However, at this point, Lock B has already been acquired by another process. 2. The second process (Process 2) enters the hugetlb_fault handler during the unmap operation. It successfully acquires Lock B (hugetlb_fault_mutex_table lock) that was just released by Process 1, but then attempts to acquire Lock A (pagecache_folio lock), which is still held by Process 1. As a result, Process 1 (holding Lock A) is blocked waiting for Lock B (held by Process 2), while Process 2 (holding Lock B) is blocked waiting for Lock A (held by Process 1), constructing a ABBA deadlock scenario. The solution here is to unlock the pagecache_folio and provide the pagecache_folio_unlocked variable to the caller to have the visibility over the pagecache_folio status for subsequent handling. The error message: INFO: task repro_20250402_:13229 blocked for more than 64 seconds. Not tainted 6.15.0-rc3+ #24 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:repro_20250402_ state:D stack:25856 pid:13229 tgid:13228 ppid:3513 task_flags:0x400040 flags:0x00004006 Call Trace: __schedule+0x1755/0x4f50 schedule+0x158/0x330 schedule_preempt_disabled+0x15/0x30 __mutex_lock+0x75f/0xeb0 hugetlb_wp+0xf88/0x3440 hugetlb_fault+0x14c8/0x2c30 trace_clock_x86_tsc+0x20/0x20 do_user_addr_fault+0x61d/0x1490 exc_page_fault+0x64/0x100 asm_exc_page_fault+0x26/0x30 RIP: 0010:__put_user_4+0xd/0x20 copy_process+0x1f4a/0x3d60 kernel_clone+0x210/0x8f0 __x64_sys_clone+0x18d/0x1f0 do_syscall_64+0x6a/0x120 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x41b26d INFO: task repro_20250402_:13229 is blocked on a mutex likely owned by task repro_20250402_:13250. task:repro_20250402_ state:D stack:28288 pid:13250 tgid:13228 ppid:3513 task_flags:0x400040 flags:0x00000006 Call Trace: __schedule+0x1755/0x4f50 schedule+0x158/0x330 io_schedule+0x92/0x110 folio_wait_bit_common+0x69a/0xba0 __filemap_get_folio+0x154/0xb70 hugetlb_fault+0xa50/0x2c30 trace_clock_x86_tsc+0x20/0x20 do_user_addr_fault+0xace/0x1490 exc_page_fault+0x64/0x100 asm_exc_page_fault+0x26/0x30 RIP: 0033:0x402619 INFO: task repro_20250402_:13250 blocked for more than 65 seconds. Not tainted 6.15.0-rc3+ #24 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:repro_20250402_ state:D stack:28288 pid:13250 tgid:13228 ppid:3513 task_flags:0x400040 flags:0x00000006 Call Trace: __schedule+0x1755/0x4f50 schedule+0x158/0x330 io_schedule+0x92/0x110 folio_wait_bit_common+0x69a/0xba0 __filemap_get_folio+0x154/0xb70 hugetlb_fault+0xa50/0x2c30 trace_clock_x86_tsc+0x20/0x20 do_user_addr_fault+0xace/0x1490 exc_page_fault+0x64/0x100 asm_exc_page_fault+0x26/0x30 RIP: 0033:0x402619 Showing all locks held in the system: 1 lock held by khungtaskd/35: #0: ffffffff879a7440 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x30/0x180 2 locks held by repro_20250402_/13229: #0: ffff888017d801e0 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x37/0x300 #1: ffff888000fec848 (&hugetlb_fault_mutex_table[i]){+.+.}-{4:4}, at: hugetlb_wp+0xf88/0x3440 3 locks held by repro_20250402_/13250: #0: ffff8880177f3d08 (vm_lock){++++}-{0:0}, at: do_user_addr_fault+0x41b/0x1490 #1: ffff888000fec848 (&hugetlb_fault_mutex_table[i]){+.+.}-{4:4}, at: hugetlb_fault+0x3b8/0x2c30 #2: ffff8880129500e8 (&resv_map->rw_sema){++++}-{4:4}, at: hugetlb_fault+0x494/0x2c30 Link: https://drive.google.com/file/d/1DVRnIW-vSayU5J1re9Ct_br3jJQU6Vpb/view?usp=drive_link [1] Link: https://github.com/bboymimi/bpftracer/blob/master/scripts/hugetlb_lock_debug.bt [2] Link: https://drive.google.com/file/d/1bWq2-8o-BJAuhoHWX7zAhI6ggfhVzQUI/view?usp=sharing [3] Link: https://lkml.kernel.org/r/20250513093448.592150-1-gavinguo@igalia.com Fixes: 40549ba8f8e0 ("hugetlb: use new vma_lock for pmd sharing synchronization") Signed-off-by: Gavin Guo Cc: Hugh Dickins Cc: Florent Revest Cc: Gavin Shan Cc: Muchun Song Cc: Oscar Salvador Cc: Byungchul Park Cc: Signed-off-by: Andrew Morton --- mm/hugetlb.c | 33 ++++++++++++++++++++++++++++----- 1 file changed, 28 insertions(+), 5 deletions(-) --- a/mm/hugetlb.c~mm-hugetlb-fix-a-deadlock-with-pagecache_folio-and-hugetlb_fault_mutex_table +++ a/mm/hugetlb.c @@ -6131,7 +6131,8 @@ static void unmap_ref_private(struct mm_ * Keep the pte_same checks anyway to make transition from the mutex easier. */ static vm_fault_t hugetlb_wp(struct folio *pagecache_folio, - struct vm_fault *vmf) + struct vm_fault *vmf, + bool *pagecache_folio_unlocked) { struct vm_area_struct *vma = vmf->vma; struct mm_struct *mm = vma->vm_mm; @@ -6229,6 +6230,22 @@ retry_avoidcopy: folio_put(old_folio); /* + * The pagecache_folio needs to be unlocked to avoid + * deadlock and we won't re-lock it in hugetlb_wp(). The + * pagecache_folio could be truncated after being + * unlocked. So its state should not be relied + * subsequently. + * + * Setting *pagecache_folio_unlocked to true allows the + * caller to handle any necessary logic related to the + * folio's unlocked state. + */ + if (pagecache_folio) { + folio_unlock(pagecache_folio); + if (pagecache_folio_unlocked) + *pagecache_folio_unlocked = true; + } + /* * Drop hugetlb_fault_mutex and vma_lock before * unmapping. unmapping needs to hold vma_lock * in write mode. Dropping vma_lock in read mode @@ -6581,7 +6598,7 @@ static vm_fault_t hugetlb_no_page(struct hugetlb_count_add(pages_per_huge_page(h), mm); if ((vmf->flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) { /* Optimization, do the COW without a second fault */ - ret = hugetlb_wp(folio, vmf); + ret = hugetlb_wp(folio, vmf, NULL); } spin_unlock(vmf->ptl); @@ -6653,6 +6670,7 @@ vm_fault_t hugetlb_fault(struct mm_struc struct hstate *h = hstate_vma(vma); struct address_space *mapping; int need_wait_lock = 0; + bool pagecache_folio_unlocked = false; struct vm_fault vmf = { .vma = vma, .address = address & huge_page_mask(h), @@ -6807,7 +6825,8 @@ vm_fault_t hugetlb_fault(struct mm_struc if (flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) { if (!huge_pte_write(vmf.orig_pte)) { - ret = hugetlb_wp(pagecache_folio, &vmf); + ret = hugetlb_wp(pagecache_folio, &vmf, + &pagecache_folio_unlocked); goto out_put_page; } else if (likely(flags & FAULT_FLAG_WRITE)) { vmf.orig_pte = huge_pte_mkdirty(vmf.orig_pte); @@ -6824,10 +6843,14 @@ out_put_page: out_ptl: spin_unlock(vmf.ptl); - if (pagecache_folio) { + /* + * If the pagecache_folio is unlocked in hugetlb_wp(), we skip + * folio_unlock() here. + */ + if (pagecache_folio && !pagecache_folio_unlocked) folio_unlock(pagecache_folio); + if (pagecache_folio) folio_put(pagecache_folio); - } out_mutex: hugetlb_vma_unlock_read(vma); _ Patches currently in -mm which might be from gavinguo@igalia.com are