April 2025 - Linux-stable-mirror

[PATCH] media: gspca: Add error handling for stv06xx_read_sensor()

by Wentao Liang

In hdcs_init(), the return value of stv06xx_read_sensor() needs to be checked. A proper implementation can be found in vv6410_dump(). Add a check in loop condition and propergate error code to fix this issue. Fixes: 4c98834addfe ("V4L/DVB (10048): gspca - stv06xx: New subdriver.") Cc: stable(a)vger.kernel.org # v2.6+ Signed-off-by: Wentao Liang <vulab(a)iscas.ac.cn> --- drivers/media/usb/gspca/stv06xx/stv06xx_hdcs.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/media/usb/gspca/stv06xx/stv06xx_hdcs.c b/drivers/media/usb/gspca/stv06xx/stv06xx_hdcs.c index 5a47dcbf1c8e..303b055fefea 100644 --- a/drivers/media/usb/gspca/stv06xx/stv06xx_hdcs.c +++ b/drivers/media/usb/gspca/stv06xx/stv06xx_hdcs.c @@ -520,12 +520,13 @@ static int hdcs_init(struct sd *sd) static int hdcs_dump(struct sd *sd) { u16 reg, val; + int err = 0; pr_info("Dumping sensor registers:\n"); - for (reg = HDCS_IDENT; reg <= HDCS_ROWEXPH; reg++) { - stv06xx_read_sensor(sd, reg, &val); + for (reg = HDCS_IDENT; reg <= HDCS_ROWEXPH && !err; reg++) { + err = stv06xx_read_sensor(sd, reg, &val); pr_info("reg 0x%02x = 0x%02x\n", reg, val); } - return 0; + return (err < 0) ? err : 0; } -- 2.42.0.windows.2

8 months

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[for-linus][PATCH 4/4] tracing: Verify event formats that have "%*p.."

by Steven Rostedt

From: Steven Rostedt <rostedt(a)goodmis.org> The trace event verifier checks the formats of trace events to make sure that they do not point at memory that is not in the trace event itself or in data that will never be freed. If an event references data that was allocated when the event triggered and that same data is freed before the event is read, then the kernel can crash by reading freed memory. The verifier runs at boot up (or module load) and scans the print formats of the events and checks their arguments to make sure that dereferenced pointers are safe. If the format uses "%*p.." the verifier will ignore it, and that could be dangerous. Cover this case as well. Also add to the sample code a use case of "%*pbl". Link: https://lore.kernel.org/all/bcba4d76-2c3f-4d11-baf0-02905db953dd@oracle.com/ Cc: stable(a)vger.kernel.org Cc: Masami Hiramatsu <mhiramat(a)kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers(a)efficios.com> Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers") Link: https://lore.kernel.org/20250327195311.2d89ec66@gandalf.local.home Reported-by: Libo Chen <libo.chen(a)oracle.com> Reviewed-by: Libo Chen <libo.chen(a)oracle.com> Tested-by: Libo Chen <libo.chen(a)oracle.com> Signed-off-by: Steven Rostedt (Google) <rostedt(a)goodmis.org> --- kernel/trace/trace_events.c | 7 +++++++ samples/trace_events/trace-events-sample.h | 8 ++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 8638b7f7ff85..069e92856bda 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -470,6 +470,7 @@ static void test_event_printk(struct trace_event_call *call) case '%': continue; case 'p': + do_pointer: /* Find dereferencing fields */ switch (fmt[i + 1]) { case 'B': case 'R': case 'r': @@ -498,6 +499,12 @@ static void test_event_printk(struct trace_event_call *call) continue; if (fmt[i + j] == '*') { star = true; + /* Handle %*pbl case */ + if (!j && fmt[i + 1] == 'p') { + arg++; + i++; + goto do_pointer; + } continue; } if ((fmt[i + j] == 's')) { diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h index 999f78d380ae..1a05fc153353 100644 --- a/samples/trace_events/trace-events-sample.h +++ b/samples/trace_events/trace-events-sample.h @@ -319,7 +319,8 @@ TRACE_EVENT(foo_bar, __assign_cpumask(cpum, cpumask_bits(mask)); ), - TP_printk("foo %s %d %s %s %s %s %s %s (%s) (%s) %s", __entry->foo, __entry->bar, + TP_printk("foo %s %d %s %s %s %s %s %s (%s) (%s) %s [%d] %*pbl", + __entry->foo, __entry->bar, /* * Notice here the use of some helper functions. This includes: @@ -370,7 +371,10 @@ TRACE_EVENT(foo_bar, __get_str(str), __get_str(lstr), __get_bitmask(cpus), __get_cpumask(cpum), - __get_str(vstr)) + __get_str(vstr), + __get_dynamic_array_len(cpus), + __get_dynamic_array_len(cpus), + __get_dynamic_array(cpus)) ); /* -- 2.47.2

8 months

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[for-linus][PATCH 3/4] ftrace: Add cond_resched() to ftrace_graph_set_hash()

by Steven Rostedt

From: zhoumin <teczm(a)foxmail.com> When the kernel contains a large number of functions that can be traced, the loop in ftrace_graph_set_hash() may take a lot of time to execute. This may trigger the softlockup watchdog. Add cond_resched() within the loop to allow the kernel to remain responsive even when processing a large number of functions. This matches the cond_resched() that is used in other locations of the code that iterates over all functions that can be traced. Cc: stable(a)vger.kernel.org Fixes: b9b0c831bed26 ("ftrace: Convert graph filter to use hash tables") Link: https://lore.kernel.org/tencent_3E06CE338692017B5809534B9C5C03DA7705@qq.com Signed-off-by: zhoumin <teczm(a)foxmail.com> Signed-off-by: Steven Rostedt (Google) <rostedt(a)goodmis.org> --- kernel/trace/ftrace.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 92015de6203d..1a48aedb5255 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6855,6 +6855,7 @@ ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer) } } } + cond_resched(); } while_for_each_ftrace_rec(); return fail ? -EINVAL : 0; -- 2.47.2

8 months

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[PATCH v2] usb: dwc3: gadget: check that event count does not exceed event buffer length

by Frode Isaksen

From: Frode Isaksen <frode(a)meta.com> The event count is read from register DWC3_GEVNTCOUNT. There is a check for the count being zero, but not for exceeding the event buffer length. Check that event count does not exceed event buffer length, avoiding an out-of-bounds access when memcpy'ing the event. Crash log: Unable to handle kernel paging request at virtual address ffffffc0129be000 pc : __memcpy+0x114/0x180 lr : dwc3_check_event_buf+0xec/0x348 x3 : 0000000000000030 x2 : 000000000000dfc4 x1 : ffffffc0129be000 x0 : ffffff87aad60080 Call trace: __memcpy+0x114/0x180 dwc3_interrupt+0x24/0x34 Signed-off-by: Frode Isaksen <frode(a)meta.com> Fixes: ebbb2d59398f ("usb: dwc3: gadget: use evt->cache for processing events") Cc: stable(a)vger.kernel.org --- v1->v2: added error log drivers/usb/dwc3/gadget.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c index 89a4dc8ebf94..923737776d82 100644 --- a/drivers/usb/dwc3/gadget.c +++ b/drivers/usb/dwc3/gadget.c @@ -4564,6 +4564,12 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt) if (!count) return IRQ_NONE; + if (count > evt->length) { + dev_err(dwc->dev, "invalid count(%u) > evt->length(%u)\n", + count, evt->length); + return IRQ_NONE; + } + evt->count = count; evt->flags |= DWC3_EVENT_PENDING; -- 2.49.0

8 months

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[PATCH 3/4] drm/i915/gem: Allow EXEC_CAPTURE on recoverable contexts on DG1

by Ville Syrjala

From: Ville Syrjälä <ville.syrjala(a)linux.intel.com> The intel-media-driver is currently broken on DG1 because it uses EXEC_CAPTURE with recovarable contexts. Relax the check to allow that. I've also submitted a fix for the intel-media-driver: https://github.com/intel/media-driver/pull/1920 Cc: stable(a)vger.kernel.org Cc: Matthew Auld <matthew.auld(a)intel.com> Cc: Thomas Hellström <thomas.hellstrom(a)linux.intel.com> Fixes: 71b1669ea9bd ("drm/i915/uapi: tweak error capture on recoverable contexts") Signed-off-by: Ville Syrjälä <ville.syrjala(a)linux.intel.com> --- drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c index ca7e9216934a..ea9d5063ce78 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c @@ -2013,7 +2013,7 @@ static int eb_capture_stage(struct i915_execbuffer *eb) continue; if (i915_gem_context_is_recoverable(eb->gem_context) && - (IS_DGFX(eb->i915) || GRAPHICS_VER_FULL(eb->i915) > IP_VER(12, 0))) + GRAPHICS_VER_FULL(eb->i915) > IP_VER(12, 10)) return -EINVAL; for_each_batch_create_order(eb, j) { -- 2.45.3

8 months

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[PATCH v5 4/4] ring-buffer: Use flush_kernel_vmap_range() over flush_dcache_folio()

by Steven Rostedt

From: Steven Rostedt <rostedt(a)goodmis.org> Some architectures do not have data cache coherency between user and kernel space. For these architectures, the cache needs to be flushed on both the kernel and user addresses so that user space can see the updates the kernel has made. Instead of using flush_dcache_folio() and playing with virt_to_folio() within the call to that function, use flush_kernel_vmap_range() which takes the virtual address and does the work for those architectures that need it. This also fixes a bug where the flush of the reader page only flushed one page. If the sub-buffer order is 1 or more, where the sub-buffer size would be greater than a page, it would miss the rest of the sub-buffer content, as the "reader page" is not just a page, but the size of a sub-buffer. Link: https://lore.kernel.org/all/CAG48ez3w0my4Rwttbc5tEbNsme6tc0mrSN95thjXUFaJ3a… Cc: stable(a)vger.kernel.org Fixes: 117c39200d9d7 ("ring-buffer: Introducing ring-buffer mapping functions"); Suggested-by: Jann Horn <jannh(a)google.com> Signed-off-by: Steven Rostedt (Google) <rostedt(a)goodmis.org> --- kernel/trace/ring_buffer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index d8d7b28e2c2f..c0f877d39a24 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6016,7 +6016,7 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) meta->read = cpu_buffer->read; /* Some archs do not have data cache coherency between kernel and user-space */ - flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page)); + flush_kernel_vmap_range(cpu_buffer->meta_page, PAGE_SIZE); } static void @@ -7319,7 +7319,8 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu) out: /* Some archs do not have data cache coherency between kernel and user-space */ - flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page)); + flush_kernel_vmap_range(cpu_buffer->reader_page->page, + buffer->subbuf_size + BUF_PAGE_HDR_SIZE); rb_update_meta_page(cpu_buffer); -- 2.47.2

8 months

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[merged mm-nonmm-stable] lib-scatterlist-fix-sg_split_phys-to-preserve-original-scatterlist-offsets.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: lib: scatterlist: fix sg_split_phys to preserve original scatterlist offsets has been removed from the -mm tree. Its filename was lib-scatterlist-fix-sg_split_phys-to-preserve-original-scatterlist-offsets.patch This patch was dropped because it was merged into the mm-nonmm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: T Pratham <t-pratham(a)ti.com> Subject: lib: scatterlist: fix sg_split_phys to preserve original scatterlist offsets Date: Wed, 19 Mar 2025 16:44:38 +0530 The split_sg_phys function was incorrectly setting the offsets of all scatterlist entries (except the first) to 0. Only the first scatterlist entry's offset and length needs to be modified to account for the skip. Setting the rest entries' offsets to 0 could lead to incorrect data access. I am using this function in a crypto driver that I'm currently developing (not yet sent to mailing list). During testing, it was observed that the output scatterlists (except the first one) contained incorrect garbage data. I narrowed this issue down to the call of sg_split(). Upon debugging inside this function, I found that this resetting of offset is the cause of the problem, causing the subsequent scatterlists to point to incorrect memory locations in a page. By removing this code, I am obtaining expected data in all the split output scatterlists. Thus, this was indeed causing observable runtime effects! This patch removes the offending code, ensuring that the page offsets in the input scatterlist are preserved in the output scatterlist. Link: https://lkml.kernel.org/r/20250319111437.1969903-1-t-pratham@ti.com Fixes: f8bcbe62acd0 ("lib: scatterlist: add sg splitting function") Signed-off-by: T Pratham <t-pratham(a)ti.com> Cc: Robert Jarzmik <robert.jarzmik(a)free.fr> Cc: Jens Axboe <axboe(a)kernel.dk> Cc: Kamlesh Gurudasani <kamlesh(a)ti.com> Cc: Praneeth Bajjuri <praneeth(a)ti.com> Cc: Vignesh Raghavendra <vigneshr(a)ti.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- lib/sg_split.c | 2 -- 1 file changed, 2 deletions(-) --- a/lib/sg_split.c~lib-scatterlist-fix-sg_split_phys-to-preserve-original-scatterlist-offsets +++ a/lib/sg_split.c @@ -88,8 +88,6 @@ static void sg_split_phys(struct sg_spli if (!j) { out_sg->offset += split->skip_sg0; out_sg->length -= split->skip_sg0; - } else { - out_sg->offset = 0; } sg_dma_address(out_sg) = 0; sg_dma_len(out_sg) = 0; _ Patches currently in -mm which might be from t-pratham(a)ti.com are

8 months

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[merged mm-hotfixes-stable] mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead() has been removed from the -mm tree. Its filename was mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Yosry Ahmed <yosry.ahmed(a)linux.dev> Subject: mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead() Date: Wed, 26 Feb 2025 18:56:25 +0000 Currently, zswap_cpu_comp_dead() calls crypto_free_acomp() while holding the per-CPU acomp_ctx mutex. crypto_free_acomp() then holds scomp_lock (through crypto_exit_scomp_ops_async()). On the other hand, crypto_alloc_acomp_node() holds the scomp_lock (through crypto_scomp_init_tfm()), and then allocates memory. If the allocation results in reclaim, we may attempt to hold the per-CPU acomp_ctx mutex. The above dependencies can cause an ABBA deadlock. For example in the following scenario: (1) Task A running on CPU #1: crypto_alloc_acomp_node() Holds scomp_lock Enters reclaim Reads per_cpu_ptr(pool->acomp_ctx, 1) (2) Task A is descheduled (3) CPU #1 goes offline zswap_cpu_comp_dead(CPU #1) Holds per_cpu_ptr(pool->acomp_ctx, 1)) Calls crypto_free_acomp() Waits for scomp_lock (4) Task A running on CPU #2: Waits for per_cpu_ptr(pool->acomp_ctx, 1) // Read on CPU #1 DEADLOCK Since there is no requirement to call crypto_free_acomp() with the per-CPU acomp_ctx mutex held in zswap_cpu_comp_dead(), move it after the mutex is unlocked. Also move the acomp_request_free() and kfree() calls for consistency and to avoid any potential sublte locking dependencies in the future. With this, only setting acomp_ctx fields to NULL occurs with the mutex held. This is similar to how zswap_cpu_comp_prepare() only initializes acomp_ctx fields with the mutex held, after performing all allocations before holding the mutex. Opportunistically, move the NULL check on acomp_ctx so that it takes place before the mutex dereference. Link: https://lkml.kernel.org/r/20250226185625.2672936-1-yosry.ahmed@linux.dev Fixes: 12dcb0ef5406 ("mm: zswap: properly synchronize freeing resources during CPU hotunplug") Signed-off-by: Herbert Xu <herbert(a)gondor.apana.org.au> Co-developed-by: Herbert Xu <herbert(a)gondor.apana.org.au> Signed-off-by: Yosry Ahmed <yosry.ahmed(a)linux.dev> Reported-by: syzbot+1a517ccfcbc6a7ab0f82(a)syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67bcea51.050a0220.bbfd1.0096.GAE@google.com/ Acked-by: Herbert Xu <herbert(a)gondor.apana.org.au> Reviewed-by: Chengming Zhou <chengming.zhou(a)linux.dev> Reviewed-by: Nhat Pham <nphamcs(a)gmail.com> Tested-by: Nhat Pham <nphamcs(a)gmail.com> Cc: David S. Miller <davem(a)davemloft.net> Cc: Eric Biggers <ebiggers(a)kernel.org> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: Chris Murphy <lists(a)colorremedies.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/zswap.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) --- a/mm/zswap.c~mm-zswap-fix-crypto_free_acomp-deadlock-in-zswap_cpu_comp_dead +++ a/mm/zswap.c @@ -883,18 +883,32 @@ static int zswap_cpu_comp_dead(unsigned { struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node); struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu); + struct acomp_req *req; + struct crypto_acomp *acomp; + u8 *buffer; + + if (IS_ERR_OR_NULL(acomp_ctx)) + return 0; mutex_lock(&acomp_ctx->mutex); - if (!IS_ERR_OR_NULL(acomp_ctx)) { - if (!IS_ERR_OR_NULL(acomp_ctx->req)) - acomp_request_free(acomp_ctx->req); - acomp_ctx->req = NULL; - if (!IS_ERR_OR_NULL(acomp_ctx->acomp)) - crypto_free_acomp(acomp_ctx->acomp); - kfree(acomp_ctx->buffer); - } + req = acomp_ctx->req; + acomp = acomp_ctx->acomp; + buffer = acomp_ctx->buffer; + acomp_ctx->req = NULL; + acomp_ctx->acomp = NULL; + acomp_ctx->buffer = NULL; mutex_unlock(&acomp_ctx->mutex); + /* + * Do the actual freeing after releasing the mutex to avoid subtle + * locking dependencies causing deadlocks. + */ + if (!IS_ERR_OR_NULL(req)) + acomp_request_free(req); + if (!IS_ERR_OR_NULL(acomp)) + crypto_free_acomp(acomp); + kfree(buffer); + return 0; } _ Patches currently in -mm which might be from yosry.ahmed(a)linux.dev are

8 months

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[merged mm-hotfixes-stable] mm-hugetlb-move-hugetlb_sysctl_init-to-the-__init-section.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: mm/hugetlb: move hugetlb_sysctl_init() to the __init section has been removed from the -mm tree. Its filename was mm-hugetlb-move-hugetlb_sysctl_init-to-the-__init-section.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Marc Herbert <Marc.Herbert(a)linux.intel.com> Subject: mm/hugetlb: move hugetlb_sysctl_init() to the __init section Date: Wed, 19 Mar 2025 06:00:30 +0000 hugetlb_sysctl_init() is only invoked once by an __init function and is merely a wrapper around another __init function so there is not reason to keep it. Fixes the following warning when toning down some GCC inline options: WARNING: modpost: vmlinux: section mismatch in reference: hugetlb_sysctl_init+0x1b (section: .text) -> __register_sysctl_init (section: .init.text) Link: https://lkml.kernel.org/r/20250319060041.2737320-1-marc.herbert@linux.intel… Signed-off-by: Marc Herbert <Marc.Herbert(a)linux.intel.com> Reviewed-by: Anshuman Khandual <anshuman.khandual(a)arm.com> Reviewed-by: Muchun Song <muchun.song(a)linux.dev> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- mm/hugetlb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/hugetlb.c~mm-hugetlb-move-hugetlb_sysctl_init-to-the-__init-section +++ a/mm/hugetlb.c @@ -5179,7 +5179,7 @@ static const struct ctl_table hugetlb_ta }, }; -static void hugetlb_sysctl_init(void) +static void __init hugetlb_sysctl_init(void) { register_sysctl_init("vm", hugetlb_table); } _ Patches currently in -mm which might be from Marc.Herbert(a)linux.intel.com are

8 months

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[merged mm-hotfixes-stable] mm-userfaultfd-fix-release-hang-over-concurrent-gup.patch removed from -mm tree

by Andrew Morton

The quilt patch titled Subject: mm/userfaultfd: fix release hang over concurrent GUP has been removed from the -mm tree. Its filename was mm-userfaultfd-fix-release-hang-over-concurrent-gup.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Peter Xu <peterx(a)redhat.com> Subject: mm/userfaultfd: fix release hang over concurrent GUP Date: Wed, 12 Mar 2025 10:51:31 -0400 This patch should fix a possible userfaultfd release() hang during concurrent GUP. This problem was initially reported by Dimitris Siakavaras in July 2023 [1] in a firecracker use case. Firecracker has a separate process handling page faults remotely, and when the process releases the userfaultfd it can race with a concurrent GUP from KVM trying to fault in a guest page during the secondary MMU page fault process. A similar problem was reported recently again by Jinjiang Tu in March 2025 [2], even though the race happened this time with a mlockall() operation, which does GUP in a similar fashion. In 2017, commit 656710a60e36 ("userfaultfd: non-cooperative: closing the uffd without triggering SIGBUS") was trying to fix this issue. AFAIU, that fixes well the fault paths but may not work yet for GUP. In GUP, the issue is NOPAGE will be almost treated the same as "page fault resolved" in faultin_page(), then the GUP will follow page again, seeing page missing, and it'll keep going into a live lock situation as reported. This change makes core mm return RETRY instead of NOPAGE for both the GUP and fault paths, proactively releasing the mmap read lock. This should guarantee the other release thread make progress on taking the write lock and avoid the live lock even for GUP. When at it, rearrange the comments to make sure it's uptodate. [1] https://lore.kernel.org/r/79375b71-db2e-3e66-346b-254c90d915e2@cslab.ece.nt… [2] https://lore.kernel.org/r/20250307072133.3522652-1-tujinjiang@huawei.com Link: https://lkml.kernel.org/r/20250312145131.1143062-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx(a)redhat.com> Cc: Andrea Arcangeli <aarcange(a)redhat.com> Cc: Mike Rapoport (IBM) <rppt(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Jinjiang Tu <tujinjiang(a)huawei.com> Cc: Dimitris Siakavaras <jimsiak(a)cslab.ece.ntua.gr> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> --- fs/userfaultfd.c | 51 ++++++++++++++++++++++----------------------- 1 file changed, 25 insertions(+), 26 deletions(-) --- a/fs/userfaultfd.c~mm-userfaultfd-fix-release-hang-over-concurrent-gup +++ a/fs/userfaultfd.c @@ -396,32 +396,6 @@ vm_fault_t handle_userfault(struct vm_fa goto out; /* - * If it's already released don't get it. This avoids to loop - * in __get_user_pages if userfaultfd_release waits on the - * caller of handle_userfault to release the mmap_lock. - */ - if (unlikely(READ_ONCE(ctx->released))) { - /* - * Don't return VM_FAULT_SIGBUS in this case, so a non - * cooperative manager can close the uffd after the - * last UFFDIO_COPY, without risking to trigger an - * involuntary SIGBUS if the process was starting the - * userfaultfd while the userfaultfd was still armed - * (but after the last UFFDIO_COPY). If the uffd - * wasn't already closed when the userfault reached - * this point, that would normally be solved by - * userfaultfd_must_wait returning 'false'. - * - * If we were to return VM_FAULT_SIGBUS here, the non - * cooperative manager would be instead forced to - * always call UFFDIO_UNREGISTER before it can safely - * close the uffd. - */ - ret = VM_FAULT_NOPAGE; - goto out; - } - - /* * Check that we can return VM_FAULT_RETRY. * * NOTE: it should become possible to return VM_FAULT_RETRY @@ -457,6 +431,31 @@ vm_fault_t handle_userfault(struct vm_fa if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) goto out; + if (unlikely(READ_ONCE(ctx->released))) { + /* + * If a concurrent release is detected, do not return + * VM_FAULT_SIGBUS or VM_FAULT_NOPAGE, but instead always + * return VM_FAULT_RETRY with lock released proactively. + * + * If we were to return VM_FAULT_SIGBUS here, the non + * cooperative manager would be instead forced to + * always call UFFDIO_UNREGISTER before it can safely + * close the uffd, to avoid involuntary SIGBUS triggered. + * + * If we were to return VM_FAULT_NOPAGE, it would work for + * the fault path, in which the lock will be released + * later. However for GUP, faultin_page() does nothing + * special on NOPAGE, so GUP would spin retrying without + * releasing the mmap read lock, causing possible livelock. + * + * Here only VM_FAULT_RETRY would make sure the mmap lock + * be released immediately, so that the thread concurrently + * releasing the userfault would always make progress. + */ + release_fault_lock(vmf); + goto out; + } + /* take the reference before dropping the mmap_lock */ userfaultfd_ctx_get(ctx); _ Patches currently in -mm which might be from peterx(a)redhat.com are maintainers-add-myself-as-userfaultfd-reviewer.patch

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