From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793125144; b=y6gIKgb8tYpzWvtsnOBxWRH1MJXzd9PF9HuLgPpBokuXw/MF2IyuD73ukjhqlq/UACPI 0cabltsAE28xwFmqDvtbqdKtiPAP71Ug/dQxnHJbmX+wleOlnpuTPDDgtM7LtfJso3ZyN wTOdlIkwtJrf76UUe+iOc2eMUVoPkCMU6RetwwjMnU5Ikd9x1RPGyFzxZ9Ij9AACsTIUo NdL27kiQf7eA/opI8EKGosg5Tq/7fjE6frIhAg4htLKHgpPEktAB1iRPPZ4umISKnmfhc JOlfXnt2Rw23qo+Du3RVz/7+NbOFLxM2ydODsnUs4xT77JlK0UBuAEeY7lnpTcNGvMQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793125144; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=Um3gBd/wVu6PV095DsPLFOO4AKiu34Jab6d/B0QkhME=; b=j/DFW3cPk5nPVuNC9GDWdPOUtwqhqS+xZLd5qyhZhsDRvmBXkBwgRPGchyqvsQMiU45E 19DNz5m62uH6HQBC9TQHHpWQ78cgXM7rluv4MKlEK6H1NxzwC5r9kv7HG+E3rKSPw8ynA jFpf/OK3yQr7rRhUeBK3o+pQItYqpSyCSXwIwcXMda2eJ2J9GMZlxDl4+7WGm+/tBODPh 63kLaBu1rzZz5diKE17ljBx9iZNIo87IrjaSgj2pfk73GKiTxzFVcqUEpV1jG9+o9i4nU HjwhN1jn0E79EdFWE4WzHkud2pJ/IlhM3IkbUCz372UFAWpm3vIUD+l2tZ2vWH3DrEw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=gkYGqO+W; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BFCDC606A31A; Tue, 27 Oct 2026 18:19:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=gkYGqO+W Received: by smtp.kernel.org (Postfix) with ESMTPSA id 285501F01825; Tue, 27 Oct 2026 18:19:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793125143; bh=Um3gBd/wVu6PV095DsPLFOO4AKiu34Jab6d/B0QkhME=; h=Date:To:From:Subject; b=gkYGqO+W6GKgiYY2p7/g0WUrHcj9TKkx1CscZoxQ8Xx/SCxheIP62IdEOyCZL4XM3 ry+QPI5ej1IiBAz/bzCd914/08iHrQp1+NIP83p6j4/MgT5cKvCmPW2McPEtqLf0mK aZ2bCwdACavZMxbrNyxOI4lWJAhfbDPbEHGqhnHs= Date: Tue, 27 Oct 2026 11:19:02 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,surenb@google.com, stable@vger.kernel.org,sj@kernel.org,shakeel.butt@linux.dev,pfalcato@suse.de, liam@infradead.org,jannh@google.com,david@kernel.org,ljs@kernel.org, akpm@linux-foundation.org From: Andrew Morton Subject: + fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends.patch added to mm-unstable branch Message-Id: <20261027181903.285501F01825@smtp.kernel.org> X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The patch titled Subject: fs/proc/task_mmu: fix missed VMAs when reading /proc/PID/maps and friends has been added to the -mm mm-unstable branch. Its filename is fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Lorenzo Stoakes (ARM)" Subject: fs/proc/task_mmu: fix missed VMAs when reading /proc/PID/maps and friends Date: Tue, 27 Oct 2026 14:08:26 +0000 Reading /proc/PID/maps under per-VMA locks can skip continuously mapped address ranges during concurrent VMA splits or merges. This violates the guarantee in Documentation/filesystems/proc.rst: "If there is something at a given vaddr during the entirety of the life of the smaps/maps walk, there will be some output for it." lock_next_vma() reuses a tree iterator across calls under RCU. The iterator remembers the range of its last entry. When its node is replaced, mas_next_slot() walks the tree again at the last index of that range, then advances past the entry containing that index. If VMA boundaries changed, this can skip a range that has not been reported: - A lookup finds [A, C), then mprotect() splits it into [A, B) and [B, C) before vma_start_read() locks the first VMA. The reader reports [A, B), but the iterator still covers [A, C). The next call starts from B yet advances past C, omitting [B, C). - The reader reports [A, B) and unlocks it. A concurrent mprotect() then merges it with [B, C). On the next call, the iterator resumes at B - 1, which now belongs to [A, C), and advances past C. Again, [B, C) is lost. Checking the mmap_lock sequence only within the next call misses writers that completed before that call began. Also, a NULL result is currently accepted without validation, so a race can terminate the walk early. Even a fresh lookup can skip a mapping. Suppose it finds a gap before [B, C). A writer inserts an adjacent VMA at the end of that gap, then merges it into [B, C), replacing the node. The lookup resumes at the old gap's last index, now inside the merged VMA, and steps past it. The original [B, C) remains mapped throughout. Repeating the forward lookup is insufficient: another merge can make it skip the same mapping again, returning the same later VMA or NULL. The fresh-lookup race also affects /proc/PID/smaps, numa_maps and smaps_rollup. Resetting the iterator after gathering each VMA's statistics does not prevent a merge during the next lookup. Fixing lock_next_vma() also prevents omitted entries and incomplete rollup statistics. Tie VMA iterator state with the current mm and the write generation at the point of last mm speculation in vma_rcu_iter, whose values we call 'rvmi'. This allows us to neatly abstract the existing priv->iter logic alongside query_vma_find_by_addr() which uses its own VMA iterator. Then, provide helpers that act on the rvmi - vma_rcu_iter_[maybe_changed, may_have_skipped]() to determine whether any VMAs may have been altered since last mm speculation. Additionally introduce vma_range_is_empty(), used by vma_rcu_iter_may_have_skipped(), to determine conclusively whether VMAs exist in a set range, needing to be traversed. Original fix generated by an LLM and sent by Josef Bacik in private, then amended by David Hildenbrand, and Lorenzo Stoakes added additional abstraction. Link: https://lore.kernel.org/20261027-fix-proc-pid-maps-missing-vmas-v2-1-2791cc9fc95f@kernel.org Fixes: 5631da56c9a8 ("fs/proc/task_mmu: read proc/pid/maps under per-vma lock") Fixes: ea3085dd7a4e ("fs/proc/task_mmu: read proc/pid/{smaps|numa_maps} under per-vma lock") Fixes: 0e985559d72a ("proc/task_mmu: read proc/pid/smaps_rollup under per-vma lock") Fixes: d9d1c2d81797 ("fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks") Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Andrew Morton Co-developed-by: David Hildenbrand (Arm) Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Pedro Falcato Cc: Suren Baghdasaryan Cc: Shakeel Butt Cc: SJ Park Cc: --- fs/proc/internal.h | 1 fs/proc/task_mmu.c | 13 ++++--- include/linux/mmap_lock.h | 22 +++++++++++- mm/mmap_lock.c | 61 ++++++++++++++++++++++++++---------- 4 files changed, 72 insertions(+), 25 deletions(-) --- a/fs/proc/internal.h~fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends +++ a/fs/proc/internal.h @@ -393,6 +393,7 @@ struct proc_maps_private { struct inode *inode; struct task_struct *task; struct vma_iterator iter; + struct vma_rcu_iter rvmi; loff_t last_pos; struct proc_maps_locking_ctx lock_ctx; #ifdef CONFIG_NUMA --- a/fs/proc/task_mmu.c~fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends +++ a/fs/proc/task_mmu.c @@ -160,7 +160,7 @@ static struct vm_area_struct *get_next_v return vma_next(&priv->iter); unlock_ctx_vma(lock_ctx); - vma = lock_next_vma(lock_ctx->mm, &priv->iter, last_pos); + vma = lock_next_vma(&priv->rvmi, last_pos); if (!IS_ERR_OR_NULL(vma)) lock_ctx->locked_vma = vma; @@ -265,7 +265,7 @@ static void *m_start(struct seq_file *m, */ if (last_addr > 0) *ppos = last_addr = priv->last_pos; - vma_iter_init(&priv->iter, mm, (unsigned long)last_addr); + vma_rcu_iter_init(&priv->rvmi, mm, &priv->iter, (unsigned long)last_addr); hold_task_mempolicy(priv); /* * If seq_file had to flush its collected data right after m_next() set @@ -515,6 +515,7 @@ static struct vm_area_struct *query_vma_ struct mm_struct *mm = lock_ctx->mm; struct vm_area_struct *vma; struct vma_iterator vmi; + struct vma_rcu_iter rvmi; if (lock_ctx->mmap_locked) return find_vma(mm, addr); @@ -522,8 +523,8 @@ static struct vm_area_struct *query_vma_ /* Unlock previously locked VMA and find the next one under RCU */ unlock_ctx_vma(lock_ctx); rcu_read_lock(); - vma_iter_init(&vmi, mm, addr); - vma = lock_next_vma(mm, &vmi, addr); + vma_rcu_iter_init(&rvmi, mm, &vmi, addr); + vma = lock_next_vma(&rvmi, addr); rcu_read_unlock(); if (!vma) @@ -1416,7 +1417,7 @@ static int show_smaps_rollup(struct seq_ rcu_read_lock(); reset_lock_ctx(lock_ctx); - vma_iter_init(&priv->iter, mm, 0); + vma_rcu_iter_init(&priv->rvmi, mm, &priv->iter, 0); vma = proc_get_vma(m, &pos); if (unlikely(!vma)) goto empty_set; @@ -1465,7 +1466,7 @@ static int show_smaps_rollup(struct seq_ reset_lock_ctx(lock_ctx); /* Resume from the last position. */ pos = last_vma_end; - vma_iter_init(&priv->iter, mm, pos); + vma_rcu_iter_init(&priv->rvmi, mm, &priv->iter, pos); } vma = proc_get_vma(m, &pos); } --- a/include/linux/mmap_lock.h~fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends +++ a/include/linux/mmap_lock.h @@ -17,6 +17,13 @@ extern int rcuwait_wake_up(struct rcuwai #define MMAP_LOCK_INITIALIZER(name) \ .mmap_lock = __RWSEM_INITIALIZER((name).mmap_lock), +/* Tie a VMA iterator to mm write lock state at iterator initialisation. */ +struct vma_rcu_iter { + struct mm_struct *mm; + struct vma_iterator *vmi; + unsigned int mm_wr_seq; +}; + DECLARE_TRACEPOINT(mmap_lock_start_locking); DECLARE_TRACEPOINT(mmap_lock_acquire_returned); DECLARE_TRACEPOINT(mmap_lock_released); @@ -509,6 +516,16 @@ static inline void vma_mark_detached(str struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address); +static inline void vma_rcu_iter_init(struct vma_rcu_iter *rvmi, + struct mm_struct *mm, struct vma_iterator *vmi, + unsigned long addr) +{ + vma_iter_init(vmi, mm, addr); + rvmi->mm = mm; + rvmi->vmi = vmi; + rvmi->mm_wr_seq = UINT_MAX; /* Start odd so changed by default. */ +} + /* * Locks next vma pointed by the iterator. Confirms the locked vma has not * been modified and will retry under mmap_lock protection if modification @@ -516,9 +533,8 @@ struct vm_area_struct *lock_vma_under_rc * Returns either a valid locked VMA, NULL if no more VMAs or -EINTR if the * process was interrupted. */ -struct vm_area_struct *lock_next_vma(struct mm_struct *mm, - struct vma_iterator *iter, - unsigned long address); +struct vm_area_struct *lock_next_vma(struct vma_rcu_iter *rvmi, + unsigned long from_addr); static inline void vma_assert_can_modify(struct vm_area_struct *vma) { --- a/mm/mmap_lock.c~fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends +++ a/mm/mmap_lock.c @@ -13,6 +13,8 @@ #include #include +#include "internal.h" + EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking); EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned); EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released); @@ -428,21 +430,53 @@ static struct vm_area_struct *lock_next_ return vma; } -struct vm_area_struct *lock_next_vma(struct mm_struct *mm, - struct vma_iterator *vmi, +/* Is there no VMA in [start, last]? */ +static bool vma_range_is_empty(struct mm_struct *mm, unsigned long start, + unsigned long last) +{ + VMA_ITERATOR(vmi, mm, start); + + return !vma_iter_load(&vmi) && vma_iter_end(&vmi) - 1 >= last; +} + +/* Might the VMA tree have been modified since last mm speculation? */ +static bool vma_rcu_iter_maybe_changed(const struct vma_rcu_iter *rvmi) +{ + return (rvmi->mm_wr_seq & 1) || /* Odd implies write-lock. */ + mmap_lock_speculate_retry(rvmi->mm, rvmi->mm_wr_seq); +} + +/* Could the VMA iterator have skipped a VMA due to the tree changing? */ +static bool vma_rcu_iter_may_have_skipped(const struct vma_rcu_iter *rvmi, + unsigned long from, unsigned long to) +{ + return vma_rcu_iter_maybe_changed(rvmi) && + !vma_range_is_empty(rvmi->mm, from, to); +} + +struct vm_area_struct *lock_next_vma(struct vma_rcu_iter *rvmi, unsigned long from_addr) { + struct mm_struct *mm = rvmi->mm; + struct vma_iterator *vmi = rvmi->vmi; struct vm_area_struct *vma; - unsigned int mm_wr_seq; - bool mmap_unlocked; RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "no rcu read lock held"); retry: - /* Start mmap_lock speculation in case we need to verify the vma later */ - mmap_unlocked = mmap_lock_speculate_try_begin(mm, &mm_wr_seq); + /* Only trust the iterator's position if the tree cannot have changed. */ + if (vma_rcu_iter_maybe_changed(rvmi)) { + vma_iter_set(vmi, from_addr); + mmap_lock_speculate_try_begin(mm, &rvmi->mm_wr_seq); + } vma = vma_next(vmi); - if (!vma) - return NULL; + if (!vma) { + /* No reason to fallback if nothing left in range. */ + if (!vma_rcu_iter_may_have_skipped(rvmi, from_addr, ULONG_MAX)) + return NULL; + + rcu_read_unlock(); + goto fallback; + } vma = vma_start_read(mm, vma); if (IS_ERR_OR_NULL(vma)) { @@ -471,14 +505,9 @@ retry: * installed ahead of it. Otherwise we might observe a gap that should * not be there. */ - if (from_addr < vma->vm_start) { - /* Verify only if the address space might have changed since vma lookup. */ - if (!mmap_unlocked || mmap_lock_speculate_retry(mm, mm_wr_seq)) { - vma_iter_set(vmi, from_addr); - if (vma != vma_next(vmi)) - goto fallback_unlock; - } - } + if (from_addr < vma->vm_start && + vma_rcu_iter_may_have_skipped(rvmi, from_addr, vma->vm_start - 1)) + goto fallback_unlock; return vma; _ Patches currently in -mm which might be from ljs@kernel.org are mm-vma-fix-expansion-of-vma_mixedmap_bit-vmas.patch mm-do-not-unintentionally-overwrite-atomic-vma-flags.patch mm-vma-avoid-losing-atomic-vma-flags-when-setting-sticky-vma-flags.patch mm-vma-update-vma-iterator-state-on-error-in-new-vma-merge.patch fs-proc-task_mmu-fix-missed-vmas-when-reading-proc-pid-maps-and-friends.patch