userfaultfd: remove (VM_)BUG_ON()s

BUG_ON() is deprecated [1].  Convert all the BUG_ON()s and VM_BUG_ON()s to
use VM_WARN_ON_ONCE().

There are a few additional cases that are converted or modified:

- Convert the printk(KERN_WARNING ...) in handle_userfault() to use
  pr_warn().

- Convert the WARN_ON_ONCE()s in move_pages() to use VM_WARN_ON_ONCE(),
  as the relevant conditions are already checked in validate_range() in
  move_pages()'s caller.

- Convert the VM_WARN_ON()'s in move_pages() to VM_WARN_ON_ONCE(). These
  cases should never happen and are similar to those in mfill_atomic()
  and mfill_atomic_hugetlb(), which were previously BUG_ON()s.
  move_pages() was added later than those functions and makes use of
  VM_WARN_ON() as a replacement for the deprecated BUG_ON(), but.
  VM_WARN_ON_ONCE() is likely a better direct replacement.

- Convert the WARN_ON() for !VM_MAYWRITE in userfaultfd_unregister() and
  userfaultfd_register_range() to VM_WARN_ON_ONCE(). This condition is
  enforced in userfaultfd_register() so it should never happen, and can
  be converted to a debug check.

[1] https://www.kernel.org/doc/html/v6.15/process/coding-style.html#use-warn-rather-than-bug

Link: https://lkml.kernel.org/r/20250619-uffd-fixes-v3-3-a7274d3bd5e4@columbia.edu
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 8e7fb2a7a6aa3195bbdaf366c50f8d4b77977242..771e81ea4ef6f5fb7ca7b3a94f394ae608e32ffe 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -165,14 +165,14 @@ static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
 {
        if (refcount_dec_and_test(&ctx->refcount)) {
-               VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
-               VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
-               VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
-               VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
-               VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
-               VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
-               VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
-               VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
+               VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock));
+               VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh));
+               VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock));
+               VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh));
+               VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock));
+               VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh));
+               VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock));
+               VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh));
                mmdrop(ctx->mm);
                kmem_cache_free(userfaultfd_ctx_cachep, ctx);
        }
@@ -383,12 +383,12 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
        if (!ctx)
                goto out;
 
-       BUG_ON(ctx->mm != mm);
+       VM_WARN_ON_ONCE(ctx->mm != mm);
 
        /* Any unrecognized flag is a bug. */
-       VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
+       VM_WARN_ON_ONCE(reason & ~__VM_UFFD_FLAGS);
        /* 0 or > 1 flags set is a bug; we expect exactly 1. */
-       VM_BUG_ON(!reason || (reason & (reason - 1)));
+       VM_WARN_ON_ONCE(!reason || (reason & (reason - 1)));
 
        if (ctx->features & UFFD_FEATURE_SIGBUS)
                goto out;
@@ -411,12 +411,11 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
                 * to be sure not to return SIGBUS erroneously on
                 * nowait invocations.
                 */
-               BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
+               VM_WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
 #ifdef CONFIG_DEBUG_VM
                if (printk_ratelimit()) {
-                       printk(KERN_WARNING
-                              "FAULT_FLAG_ALLOW_RETRY missing %x\n",
-                              vmf->flags);
+                       pr_warn("FAULT_FLAG_ALLOW_RETRY missing %x\n",
+                               vmf->flags);
                        dump_stack();
                }
 #endif
@@ -602,7 +601,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
         */
 out:
        atomic_dec(&ctx->mmap_changing);
-       VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
+       VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0);
        userfaultfd_ctx_put(ctx);
 }
 
@@ -710,7 +709,7 @@ void dup_userfaultfd_fail(struct list_head *fcs)
                struct userfaultfd_ctx *ctx = fctx->new;
 
                atomic_dec(&octx->mmap_changing);
-               VM_BUG_ON(atomic_read(&octx->mmap_changing) < 0);
+               VM_WARN_ON_ONCE(atomic_read(&octx->mmap_changing) < 0);
                userfaultfd_ctx_put(octx);
                userfaultfd_ctx_put(ctx);
 
@@ -1317,8 +1316,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
        do {
                cond_resched();
 
-               BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
-                      !!(cur->vm_flags & __VM_UFFD_FLAGS));
+               VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
+                               !!(cur->vm_flags & __VM_UFFD_FLAGS));
 
                /* check not compatible vmas */
                ret = -EINVAL;
@@ -1372,7 +1371,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 
                found = true;
        } for_each_vma_range(vmi, cur, end);
-       BUG_ON(!found);
+       VM_WARN_ON_ONCE(!found);
 
        ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end,
                                         wp_async);
@@ -1464,8 +1463,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
        do {
                cond_resched();
 
-               BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
-                      !!(cur->vm_flags & __VM_UFFD_FLAGS));
+               VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
+                               !!(cur->vm_flags & __VM_UFFD_FLAGS));
 
                /*
                 * Prevent unregistering through a different userfaultfd than
@@ -1487,7 +1486,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 
                found = true;
        } for_each_vma_range(vmi, cur, end);
-       BUG_ON(!found);
+       VM_WARN_ON_ONCE(!found);
 
        vma_iter_set(&vmi, start);
        prev = vma_prev(&vmi);
@@ -1504,7 +1503,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 
                VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx != ctx);
                VM_WARN_ON_ONCE(!vma_can_userfault(vma, vma->vm_flags, wp_async));
-               WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
+               VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));
 
                if (vma->vm_start > start)
                        start = vma->vm_start;
@@ -1569,7 +1568,7 @@ static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
         * len == 0 means wake all and we don't want to wake all here,
         * so check it again to be sure.
         */
-       VM_BUG_ON(!range.len);
+       VM_WARN_ON_ONCE(!range.len);
 
        wake_userfault(ctx, &range);
        ret = 0;
@@ -1626,7 +1625,7 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
                return -EFAULT;
        if (ret < 0)
                goto out;
-       BUG_ON(!ret);
+       VM_WARN_ON_ONCE(!ret);
        /* len == 0 would wake all */
        range.len = ret;
        if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
@@ -1681,7 +1680,7 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
        if (ret < 0)
                goto out;
        /* len == 0 would wake all */
-       BUG_ON(!ret);
+       VM_WARN_ON_ONCE(!ret);
        range.len = ret;
        if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
                range.start = uffdio_zeropage.range.start;
@@ -1793,7 +1792,7 @@ static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
                goto out;
 
        /* len == 0 would wake all */
-       BUG_ON(!ret);
+       VM_WARN_ON_ONCE(!ret);
        range.len = ret;
        if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
                range.start = uffdio_continue.range.start;
@@ -1850,7 +1849,7 @@ static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long
                goto out;
 
        /* len == 0 would wake all */
-       BUG_ON(!ret);
+       VM_WARN_ON_ONCE(!ret);
        range.len = ret;
        if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
                range.start = uffdio_poison.range.start;
@@ -2111,7 +2110,7 @@ static int new_userfaultfd(int flags)
        struct file *file;
        int fd;
 
-       BUG_ON(!current->mm);
+       VM_WARN_ON_ONCE(!current->mm);
 
        /* Check the UFFD_* constants for consistency.  */
        BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 8253978ee0fb11d91128e58816ff76309ca97fac..9ff970980496459453ded6a29ad77c7f045a620e 100644 (file)
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -561,7 +561,7 @@ retry:
        }
 
        while (src_addr < src_start + len) {
-               BUG_ON(dst_addr >= dst_start + len);
+               VM_WARN_ON_ONCE(dst_addr >= dst_start + len);
 
                /*
                 * Serialize via vma_lock and hugetlb_fault_mutex.
@@ -602,7 +602,7 @@ retry:
                if (unlikely(err == -ENOENT)) {
                        up_read(&ctx->map_changing_lock);
                        uffd_mfill_unlock(dst_vma);
-                       BUG_ON(!folio);
+                       VM_WARN_ON_ONCE(!folio);
 
                        err = copy_folio_from_user(folio,
                                                   (const void __user *)src_addr, true);
@@ -614,7 +614,7 @@ retry:
                        dst_vma = NULL;
                        goto retry;
                } else
-                       BUG_ON(folio);
+                       VM_WARN_ON_ONCE(folio);
 
                if (!err) {
                        dst_addr += vma_hpagesize;
@@ -635,9 +635,9 @@ out_unlock_vma:
 out:
        if (folio)
                folio_put(folio);
-       BUG_ON(copied < 0);
-       BUG_ON(err > 0);
-       BUG_ON(!copied && !err);
+       VM_WARN_ON_ONCE(copied < 0);
+       VM_WARN_ON_ONCE(err > 0);
+       VM_WARN_ON_ONCE(!copied && !err);
        return copied ? copied : err;
 }
 #else /* !CONFIG_HUGETLB_PAGE */
@@ -711,12 +711,12 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
        /*
         * Sanitize the command parameters:
         */
-       BUG_ON(dst_start & ~PAGE_MASK);
-       BUG_ON(len & ~PAGE_MASK);
+       VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
+       VM_WARN_ON_ONCE(len & ~PAGE_MASK);
 
        /* Does the address range wrap, or is the span zero-sized? */
-       BUG_ON(src_start + len <= src_start);
-       BUG_ON(dst_start + len <= dst_start);
+       VM_WARN_ON_ONCE(src_start + len <= src_start);
+       VM_WARN_ON_ONCE(dst_start + len <= dst_start);
 
        src_addr = src_start;
        dst_addr = dst_start;
@@ -775,7 +775,7 @@ retry:
        while (src_addr < src_start + len) {
                pmd_t dst_pmdval;
 
-               BUG_ON(dst_addr >= dst_start + len);
+               VM_WARN_ON_ONCE(dst_addr >= dst_start + len);
 
                dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
                if (unlikely(!dst_pmd)) {
@@ -818,7 +818,7 @@ retry:
 
                        up_read(&ctx->map_changing_lock);
                        uffd_mfill_unlock(dst_vma);
-                       BUG_ON(!folio);
+                       VM_WARN_ON_ONCE(!folio);
 
                        kaddr = kmap_local_folio(folio, 0);
                        err = copy_from_user(kaddr,
@@ -832,7 +832,7 @@ retry:
                        flush_dcache_folio(folio);
                        goto retry;
                } else
-                       BUG_ON(folio);
+                       VM_WARN_ON_ONCE(folio);
 
                if (!err) {
                        dst_addr += PAGE_SIZE;
@@ -852,9 +852,9 @@ out_unlock:
 out:
        if (folio)
                folio_put(folio);
-       BUG_ON(copied < 0);
-       BUG_ON(err > 0);
-       BUG_ON(!copied && !err);
+       VM_WARN_ON_ONCE(copied < 0);
+       VM_WARN_ON_ONCE(err > 0);
+       VM_WARN_ON_ONCE(!copied && !err);
        return copied ? copied : err;
 }
 
@@ -940,11 +940,11 @@ int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
        /*
         * Sanitize the command parameters:
         */
-       BUG_ON(start & ~PAGE_MASK);
-       BUG_ON(len & ~PAGE_MASK);
+       VM_WARN_ON_ONCE(start & ~PAGE_MASK);
+       VM_WARN_ON_ONCE(len & ~PAGE_MASK);
 
        /* Does the address range wrap, or is the span zero-sized? */
-       BUG_ON(start + len <= start);
+       VM_WARN_ON_ONCE(start + len <= start);
 
        mmap_read_lock(dst_mm);
 
@@ -1738,15 +1738,13 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
        ssize_t moved = 0;
 
        /* Sanitize the command parameters. */
-       if (WARN_ON_ONCE(src_start & ~PAGE_MASK) ||
-           WARN_ON_ONCE(dst_start & ~PAGE_MASK) ||
-           WARN_ON_ONCE(len & ~PAGE_MASK))
-               goto out;
+       VM_WARN_ON_ONCE(src_start & ~PAGE_MASK);
+       VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
+       VM_WARN_ON_ONCE(len & ~PAGE_MASK);
 
        /* Does the address range wrap, or is the span zero-sized? */
-       if (WARN_ON_ONCE(src_start + len <= src_start) ||
-           WARN_ON_ONCE(dst_start + len <= dst_start))
-               goto out;
+       VM_WARN_ON_ONCE(src_start + len < src_start);
+       VM_WARN_ON_ONCE(dst_start + len < dst_start);
 
        err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
        if (err)
@@ -1896,9 +1894,9 @@ out_unlock:
        up_read(&ctx->map_changing_lock);
        uffd_move_unlock(dst_vma, src_vma);
 out:
-       VM_WARN_ON(moved < 0);
-       VM_WARN_ON(err > 0);
-       VM_WARN_ON(!moved && !err);
+       VM_WARN_ON_ONCE(moved < 0);
+       VM_WARN_ON_ONCE(err > 0);
+       VM_WARN_ON_ONCE(!moved && !err);
        return moved ? moved : err;
 }
 
@@ -1985,10 +1983,10 @@ int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
        for_each_vma_range(vmi, vma, end) {
                cond_resched();
 
-               BUG_ON(!vma_can_userfault(vma, vm_flags, wp_async));
-               BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
-                      vma->vm_userfaultfd_ctx.ctx != ctx);
-               WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
+               VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async));
+               VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx &&
+                               vma->vm_userfaultfd_ctx.ctx != ctx);
+               VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));
 
                /*
                 * Nothing to do: this vma is already registered into this
@@ -2064,8 +2062,8 @@ void userfaultfd_release_all(struct mm_struct *mm,
        prev = NULL;
        for_each_vma(vmi, vma) {
                cond_resched();
-               BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
-                      !!(vma->vm_flags & __VM_UFFD_FLAGS));
+               VM_WARN_ON_ONCE(!!vma->vm_userfaultfd_ctx.ctx ^
+                               !!(vma->vm_flags & __VM_UFFD_FLAGS));
                if (vma->vm_userfaultfd_ctx.ctx != ctx) {
                        prev = vma;
                        continue;