| Message ID | 20180706190658.6873-1-ross.zwisler@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 6 Jul 2018 13:06:58 -0600 Ross Zwisler <ross.zwisler@linux.intel.com> wrote: > commit 054620849110 ("mm/sparse.c: make sparse_init_one_section void and > remove check") > > changed how the error handling in sparse_add_one_section() works. > > Previously sparse_index_init() could return -EEXIST, and the function would > continue on happily. 'ret' would get unconditionally overwritten by the > result from sparse_init_one_section() and the error code after the 'out:' > label wouldn't be triggered. > > With the above referenced commit, though, an -EEXIST error return from > sparse_index_init() now takes us through the function and into the error > case after 'out:'. This eventually causes a kernel BUG, probably because > we've just freed a memory section that we successfully set up and marked as > present: Thanks. And gee it would be nice if some of this code was commented. I *assume* what's happening with that -EEXIST is that sparse_add_one_section() is discovering that the root mem_section was already initialized so things are OK. Maybe. My mind-reading skills aren't so good on Fridays. And sparse_index_init() sure looks like it needs locking to avoid races around mem_section[root]. Or perhaps we're known to be single-threaded here.
diff --git a/mm/sparse.c b/mm/sparse.c index 9574113fc745..d254bd2d3289 100644 --- a/mm/sparse.c +++ b/mm/sparse.c @@ -753,8 +753,12 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat, * plus, it does a kmalloc */ ret = sparse_index_init(section_nr, pgdat->node_id); - if (ret < 0 && ret != -EEXIST) - return ret; + if (ret < 0) { + if (ret == -EEXIST) + ret = 0; + else + return ret; + } memmap = kmalloc_section_memmap(section_nr, pgdat->node_id, altmap); if (!memmap) return -ENOMEM;
The following commit in -next: commit 054620849110 ("mm/sparse.c: make sparse_init_one_section void and remove check") changed how the error handling in sparse_add_one_section() works. Previously sparse_index_init() could return -EEXIST, and the function would continue on happily. 'ret' would get unconditionally overwritten by the result from sparse_init_one_section() and the error code after the 'out:' label wouldn't be triggered. With the above referenced commit, though, an -EEXIST error return from sparse_index_init() now takes us through the function and into the error case after 'out:'. This eventually causes a kernel BUG, probably because we've just freed a memory section that we successfully set up and marked as present: BUG: unable to handle kernel paging request at ffffea0005000080 RIP: 0010:memmap_init_zone+0x154/0x1cf Call Trace: move_pfn_range_to_zone+0x168/0x180 devm_memremap_pages+0x29b/0x480 pmem_attach_disk+0x1ae/0x6c0 [nd_pmem] ? devm_memremap+0x79/0xb0 nd_pmem_probe+0x7e/0xa0 [nd_pmem] nvdimm_bus_probe+0x6e/0x160 [libnvdimm] driver_probe_device+0x310/0x480 __device_attach_driver+0x86/0x100 ? __driver_attach+0x110/0x110 bus_for_each_drv+0x6e/0xb0 __device_attach+0xe2/0x160 device_initial_probe+0x13/0x20 bus_probe_device+0xa6/0xc0 device_add+0x41b/0x660 ? lock_acquire+0xa3/0x210 nd_async_device_register+0x12/0x40 [libnvdimm] async_run_entry_fn+0x3e/0x170 process_one_work+0x230/0x680 worker_thread+0x3f/0x3b0 kthread+0x12f/0x150 ? process_one_work+0x680/0x680 ? kthread_create_worker_on_cpu+0x70/0x70 ret_from_fork+0x3a/0x50 Fix this by clearing 'ret' back to 0 if sparse_index_init() returns -EEXIST. This restores the previous behavior. Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> --- mm/sparse.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)