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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D96DE40008 X-Stat-Signature: i9j7kc4f4cq8gjmxigd61swbnrhbpnxt X-Rspam-User: X-HE-Tag: 1747828763-700500 X-HE-Meta: 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 Piy8Wy3g 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 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: The patch fixes 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 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] Fixes: 40549ba8f8e0 ("hugetlb: use new vma_lock for pmd sharing synchronization") Cc: stable@vger.kernel.org Cc: Hugh Dickins Cc: Florent Revest Cc: Gavin Shan Suggested-by: Oscar Salvador Signed-off-by: Gavin Guo --- V1 -> V2 Suggested-by Oscar Salvador: - Use folio_test_locked to replace the unnecessary parameter passing. mm/hugetlb.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7ae38bfb9096..ed501f134eff 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6226,6 +6226,12 @@ static vm_fault_t hugetlb_wp(struct folio *pagecache_folio, u32 hash; folio_put(old_folio); + /* + * The pagecache_folio needs to be unlocked to avoid + * deadlock when the child unmaps the folio. + */ + if (pagecache_folio) + folio_unlock(pagecache_folio); /* * Drop hugetlb_fault_mutex and vma_lock before * unmapping. unmapping needs to hold vma_lock @@ -6823,8 +6829,13 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, out_ptl: spin_unlock(vmf.ptl); + /* + * hugetlb_wp() might have already unlocked pagecache_folio, so + * skip it if that is the case. + */ if (pagecache_folio) { - folio_unlock(pagecache_folio); + if (folio_test_locked(pagecache_folio)) + folio_unlock(pagecache_folio); folio_put(pagecache_folio); } out_mutex: base-commit: 4a95bc121ccdaee04c4d72f84dbfa6b880a514b6 -- 2.43.0