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[160.39.33.242]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4a779e79c12sm3794321cf.53.2025.06.19.18.24.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jun 2025 18:24:51 -0700 (PDT) From: Tal Zussman Date: Thu, 19 Jun 2025 21:24:25 -0400 Subject: [PATCH v3 3/4] userfaultfd: remove (VM_)BUG_ON()s Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250619-uffd-fixes-v3-3-a7274d3bd5e4@columbia.edu> References: <20250619-uffd-fixes-v3-0-a7274d3bd5e4@columbia.edu> In-Reply-To: <20250619-uffd-fixes-v3-0-a7274d3bd5e4@columbia.edu> To: Andrew Morton , Peter Xu , "Jason A. Donenfeld" , David Hildenbrand , Alexander Viro , Christian Brauner , Jan Kara , Andrea Arcangeli Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Tal Zussman X-Mailer: b4 0.14.3-dev-d7477 X-Developer-Signature: v=1; a=ed25519-sha256; t=1750382688; l=13816; i=tz2294@columbia.edu; s=20250528; h=from:subject:message-id; bh=owMdNBEirTOUYDKZZnWe9phYEFPqEGWEX+HWk21JD8Q=; b=1td6e7UCiOGMwEkYkMVCA0HLRM6tRyR/78GTYKhDrmwZH2WvlwjaVlh/MrbACG2gDu1MGQkz+ RX31tKbOES0APmpnf+37BCJMSX26cru2Fd6gXWzVi7Omd8r5UHX6wod X-Developer-Key: i=tz2294@columbia.edu; a=ed25519; pk=BIj5KdACscEOyAC0oIkeZqLB3L94fzBnDccEooxeM5Y= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNjIwMDAwOSBTYWx0ZWRfX77FAEwoKYOLq jxKQalxH4pO3Iu9P6GvBXR+Z0VAHNGz9YgOwnHXe7aOu6+z4qko2eKjXvwVIx8ir7jDRb9QU5Lc gDEM5drc3H194AjFIfLb5wFpdk4gbX5wlvZD1eA/2z58D7CbdZBuhmSyRQBNkIIVFz4CY9GRUp+ vPLCuDzgufMjYzQN74398vX83OyoFhFVOalxyNVgP7fAZZYCncXFjHNuvani+G12lL1oLPpyAqK zeAl+Y69erlS0J4LMQ0bbYJ1ZBEUtqY7cnxR+VBrhPIvydE0Jusxa2NkktaIjCKdyc5o51gdNGn jIbrK8lcJHXE9Sp0pMV21BNj8Xa1NA2b3RbW9LDnjdT4mWfwmiyxzww+8T+cdx8I/Gtk5YMraTm 6IHU0lRO X-Proofpoint-GUID: UbF9qaeJF9CLpKAcQiykXECmsmFwoESg X-Proofpoint-ORIG-GUID: UbF9qaeJF9CLpKAcQiykXECmsmFwoESg X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-06-19_08,2025-06-18_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=10 impostorscore=0 suspectscore=0 adultscore=0 clxscore=1015 malwarescore=0 spamscore=0 bulkscore=10 priorityscore=1501 phishscore=0 mlxlogscore=999 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2505160000 definitions=main-2506200009 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-war= n-rather-than-bug Signed-off-by: Tal Zussman --- fs/userfaultfd.c | 59 ++++++++++++++++++++++++------------------------ mm/userfaultfd.c | 68 +++++++++++++++++++++++++++-------------------------= ---- 2 files changed, 62 insertions(+), 65 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 8e7fb2a7a6aa..771e81ea4ef6 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -165,14 +165,14 @@ static void userfaultfd_ctx_get(struct userfaultfd_ct= x *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, uns= igned long reason) if (!ctx) goto out; =20 - BUG_ON(ctx->mm !=3D mm); + VM_WARN_ON_ONCE(ctx->mm !=3D mm); =20 /* 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))); =20 if (ctx->features & UFFD_FEATURE_SIGBUS) goto out; @@ -411,12 +411,11 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, uns= igned 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 us= erfaultfd_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); } =20 @@ -710,7 +709,7 @@ void dup_userfaultfd_fail(struct list_head *fcs) struct userfaultfd_ctx *ctx =3D fctx->new; =20 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); =20 @@ -1317,8 +1316,8 @@ static int userfaultfd_register(struct userfaultfd_ct= x *ctx, do { cond_resched(); =20 - 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)); =20 /* check not compatible vmas */ ret =3D -EINVAL; @@ -1372,7 +1371,7 @@ static int userfaultfd_register(struct userfaultfd_ct= x *ctx, =20 found =3D true; } for_each_vma_range(vmi, cur, end); - BUG_ON(!found); + VM_WARN_ON_ONCE(!found); =20 ret =3D 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(); =20 - 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)); =20 /* * Prevent unregistering through a different userfaultfd than @@ -1487,7 +1486,7 @@ static int userfaultfd_unregister(struct userfaultfd_= ctx *ctx, =20 found =3D true; } for_each_vma_range(vmi, cur, end); - BUG_ON(!found); + VM_WARN_ON_ONCE(!found); =20 vma_iter_set(&vmi, start); prev =3D vma_prev(&vmi); @@ -1504,7 +1503,7 @@ static int userfaultfd_unregister(struct userfaultfd_= ctx *ctx, =20 VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx !=3D 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)); =20 if (vma->vm_start > start) start =3D vma->vm_start; @@ -1569,7 +1568,7 @@ static int userfaultfd_wake(struct userfaultfd_ctx *c= tx, * len =3D=3D 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); =20 wake_userfault(ctx, &range); ret =3D 0; @@ -1626,7 +1625,7 @@ static int userfaultfd_copy(struct userfaultfd_ctx *c= tx, return -EFAULT; if (ret < 0) goto out; - BUG_ON(!ret); + VM_WARN_ON_ONCE(!ret); /* len =3D=3D 0 would wake all */ range.len =3D ret; if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { @@ -1681,7 +1680,7 @@ static int userfaultfd_zeropage(struct userfaultfd_ct= x *ctx, if (ret < 0) goto out; /* len =3D=3D 0 would wake all */ - BUG_ON(!ret); + VM_WARN_ON_ONCE(!ret); range.len =3D ret; if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { range.start =3D uffdio_zeropage.range.start; @@ -1793,7 +1792,7 @@ static int userfaultfd_continue(struct userfaultfd_ct= x *ctx, unsigned long arg) goto out; =20 /* len =3D=3D 0 would wake all */ - BUG_ON(!ret); + VM_WARN_ON_ONCE(!ret); range.len =3D ret; if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) { range.start =3D uffdio_continue.range.start; @@ -1850,7 +1849,7 @@ static inline int userfaultfd_poison(struct userfault= fd_ctx *ctx, unsigned long goto out; =20 /* len =3D=3D 0 would wake all */ - BUG_ON(!ret); + VM_WARN_ON_ONCE(!ret); range.len =3D ret; if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) { range.start =3D uffdio_poison.range.start; @@ -2111,7 +2110,7 @@ static int new_userfaultfd(int flags) struct file *file; int fd; =20 - BUG_ON(!current->mm); + VM_WARN_ON_ONCE(!current->mm); =20 /* 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 bc473ad21202..240578bed181 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -561,7 +561,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( } =20 while (src_addr < src_start + len) { - BUG_ON(dst_addr >=3D dst_start + len); + VM_WARN_ON_ONCE(dst_addr >=3D dst_start + len); =20 /* * Serialize via vma_lock and hugetlb_fault_mutex. @@ -602,7 +602,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( if (unlikely(err =3D=3D -ENOENT)) { up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); - BUG_ON(!folio); + VM_WARN_ON_ONCE(!folio); =20 err =3D copy_folio_from_user(folio, (const void __user *)src_addr, true); @@ -614,7 +614,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( dst_vma =3D NULL; goto retry; } else - BUG_ON(folio); + VM_WARN_ON_ONCE(folio); =20 if (!err) { dst_addr +=3D vma_hpagesize; @@ -635,9 +635,9 @@ static __always_inline ssize_t mfill_atomic_hugetlb( 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 us= erfaultfd_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); =20 /* Does the address range wrap, or is the span zero-sized? */ - BUG_ON(src_start + len <=3D src_start); - BUG_ON(dst_start + len <=3D dst_start); + VM_WARN_ON_ONCE(src_start + len <=3D src_start); + VM_WARN_ON_ONCE(dst_start + len <=3D dst_start); =20 src_addr =3D src_start; dst_addr =3D dst_start; @@ -775,7 +775,7 @@ static __always_inline ssize_t mfill_atomic(struct user= faultfd_ctx *ctx, while (src_addr < src_start + len) { pmd_t dst_pmdval; =20 - BUG_ON(dst_addr >=3D dst_start + len); + VM_WARN_ON_ONCE(dst_addr >=3D dst_start + len); =20 dst_pmd =3D mm_alloc_pmd(dst_mm, dst_addr); if (unlikely(!dst_pmd)) { @@ -818,7 +818,7 @@ static __always_inline ssize_t mfill_atomic(struct user= faultfd_ctx *ctx, =20 up_read(&ctx->map_changing_lock); uffd_mfill_unlock(dst_vma); - BUG_ON(!folio); + VM_WARN_ON_ONCE(!folio); =20 kaddr =3D kmap_local_folio(folio, 0); err =3D copy_from_user(kaddr, @@ -832,7 +832,7 @@ static __always_inline ssize_t mfill_atomic(struct user= faultfd_ctx *ctx, flush_dcache_folio(folio); goto retry; } else - BUG_ON(folio); + VM_WARN_ON_ONCE(folio); =20 if (!err) { dst_addr +=3D PAGE_SIZE; @@ -852,9 +852,9 @@ static __always_inline ssize_t mfill_atomic(struct user= faultfd_ctx *ctx, 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; } =20 @@ -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); =20 /* Does the address range wrap, or is the span zero-sized? */ - BUG_ON(start + len <=3D start); + VM_WARN_ON_ONCE(start + len <=3D start); =20 mmap_read_lock(dst_mm); =20 @@ -1709,15 +1709,13 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, uns= igned long dst_start, ssize_t moved =3D 0; =20 /* 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); =20 /* Does the address range wrap, or is the span zero-sized? */ - if (WARN_ON_ONCE(src_start + len <=3D src_start) || - WARN_ON_ONCE(dst_start + len <=3D dst_start)) - goto out; + VM_WARN_ON_ONCE(src_start + len < src_start); + VM_WARN_ON_ONCE(dst_start + len < dst_start); =20 err =3D uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma); if (err) @@ -1867,9 +1865,9 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsig= ned long dst_start, 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; } =20 @@ -1956,10 +1954,10 @@ int userfaultfd_register_range(struct userfaultfd_c= tx *ctx, for_each_vma_range(vmi, vma, end) { cond_resched(); =20 - BUG_ON(!vma_can_userfault(vma, vm_flags, wp_async)); - BUG_ON(vma->vm_userfaultfd_ctx.ctx && - vma->vm_userfaultfd_ctx.ctx !=3D 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 !=3D ctx); + VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE)); =20 /* * Nothing to do: this vma is already registered into this @@ -2035,8 +2033,8 @@ void userfaultfd_release_all(struct mm_struct *mm, prev =3D 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 !=3D ctx) { prev =3D vma; continue; --=20 2.39.5