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Thu, 14 May 2026 10:42:39 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 8128234456870 X-SMAIL-UIID: F00896C0358C4ED1A95DA11357443C92-20260514-104239-1 From: Hillf Danton To: Kartik Nair Cc: mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+bd6aaf99e8443d8a9034@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com Subject: Re: [PATCH] mm/hugetlb: fix deadlock in __hugetlb_zap_begin() by using trylock Date: Thu, 14 May 2026 10:42:41 +0800 Message-ID: <20260514024242.658-1-hdanton@sina.com> In-Reply-To: <20260513211927.4206-1-contact.kartikn@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 8F13940006 X-Rspam-User: X-Stat-Signature: qxuesira6pyq7fwb1ukahqeix5tsuma5 X-HE-Tag: 1778726564-634798 X-HE-Meta: U2FsdGVkX1+4cvDP66HtkBf2Olt0+V3aio8QBwmBzlaEDwasjqJKdDCKaQOsv8TGpElwBabjekh9eMinhR/8C7KzACyf0xiRaybYOik3Gd6IwPp6vSeosayU6/0wr+RFghOAWDgZcEdaSfGP5awo1YKBmsAeS7oEJnegRt9dylmATx0nCxJ4lKuUkR4Ywn3AsUGM7X6eofHv5KQMM0e8mu8fLvT0DHfy+qiDrOwm1RIMtkHK6HtGmYEP5qp7N8CnpZ62eDkIK1/HupSoGRTYtaySLAhY3j5FsFo/PIpFu2jHOroOmP8Thl5T2J2Wng416RISQfY1htzeS6lGsVQPFI6EZ9JU3B+OK3l+7Y11KgR61YpjVVCggu9y7qhOhHkCDCMW9coQVX5Q9AKXnlMPoPk0nXrROmvPXCAdAVk2YGkzV3KDDhzl5cDv4LxqJS1RRnvLBjvAGim1tyImIgB/m50ZVmDCejSpUmz9cTXJWug2vjIGAA+Aun6m/q4T6wRjdEY7cy9F6mJ+/YCk+qQOIhKDW7eG654Svy0XUIu+Ji/jWDkxltcYUo5yACuffJI4LoWmJqy3TkU2JJPYN1umf4rygTI3Dwn2AhAa0X0BiHD7DeygJQo8gWBpJwHA6t2fLfXpRGBxN5TnnGTc5gMM4LPuE2nrLVh/qK0AYfpnALO+q265pJaPQclmMoFAc3EGJoFUI4PG3kCGqFxaoLf97eG+fNEdOC8SRknVm7B95qTdiSHojoQ/GDIdOQ0Puu49GyqE7K0Aw8iSmVPalql4ixh/3dupQKw6Vcplu78nfMb4oyOQq3JvZVUzCHCuweofxgu+t5hQg9Ih7xiX+k4qOZT0VROFA6a8AKbHuqYKP1cB2JUHS7K96Go/wDOvWm3XLcON91owu6jpjmh1NZvIARo7t278AStVKB7JMkl9p6vur1ShWerUfg/aaryWgXt7iD7dNbx2+YulwKWPoZN 3BYqfi03 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 14 May 2026 02:49:27 +0530 Kartik Nair wrote: > syzbot reported a circular locking dependency involving > resv_map->rw_sema and mmap_lock: > > CPU0 CPU1 > lock(&mm->mmap_lock) > lock(sk_lock-AF_INET6) > lock(&mm->mmap_lock) > lock(&resv_map->rw_sema) > > __hugetlb_zap_begin() calls hugetlb_vma_lock_write() which does a > blocking down_write() on either vma_lock->rw_sema or > resv_map->rw_sema while mmap_lock is already held for write by the > caller chain (vm_mmap_pgoff -> mmap_region -> __mmap_region -> > unmap_region -> unmap_vmas -> hugetlb_zap_begin). > > Fix this by converting __hugetlb_zap_begin() to use > hugetlb_vma_trylock_write() instead of hugetlb_vma_lock_write(). > If the trylock fails, return false to the callers so they can skip > the zap operation safely. Update hugetlb_zap_begin() and its callers > in unmap_vmas() and zap_vma_range_batched() accordingly. > Given q->q_usage_counter in the syzbot report [1] and the correct locking order in ffa1e7ada456 ("block: Make request_queue lockdep splats show up earlier"), I suspect change to hugetlb is needed. [1] https://lore.kernel.org/lkml/6a02edcf.170a0220.7f9b3.000c.GAE@google.com/