[to-be-updated] mm-hugetlb-fix-a-deadlock-with-pagecache_folio-and-hugetlb_fault_mutex_table.patch removed from -mm tree

[to-be-updated] mm-hugetlb-fix-a-deadlock-with-pagecache_folio-and-hugetlb_fault_mutex_table.patch removed from -mm tree

[Andrew Morton]

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 <gavinguo@igalia.com>
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:
 <TASK>
 __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
 </TASK>
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:
 <TASK>
 __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
 </TASK>
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:
 <TASK>
 __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
 </TASK>

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 <gavinguo@igalia.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Florent Revest <revest@google.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Byungchul Park <byungchul@sk.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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