On Thu, Oct 22, 2015 at 10:24:33AM +0200, Artem Savkov wrote: > On Tue, Oct 06, 2015 at 06:23:41PM +0300, Kirill A. Shutemov wrote: > > With new THP refcounting, we don't need tricks to stabilize huge page. > > If we've got reference to tail page, it can't split under us. > > > > This patch effectively reverts a5b338f2b0b1. > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > > Tested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > > Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx> > > --- > > kernel/futex.c | 61 ++++++++++++---------------------------------------------- > > 1 file changed, 12 insertions(+), 49 deletions(-) > > This patch breaks compound page futexes with the following panic: > > [ 33.465456] general protection fault: 0000 [#1] SMP > [ 33.465991] CPU: 1 PID: 523 Comm: tst Not tainted 4.3.0-rc6-next-20151022 #139 > [ 33.466585] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140709_153950- 04/01/2014 > [ 33.467370] task: ffff88007bf13a80 ti: ffff88006bdac000 task.ti: ffff88006bdac000 > [ 33.467960] RIP: 0010:[<ffffffff81132b3a>] [<ffffffff81132b3a>] get_futex_key+0x2ba/0x410 > [ 33.468332] RSP: 0018:ffff88006bdafc18 EFLAGS: 00010202 > [ 33.468332] RAX: dead000000000000 RBX: ffffea0001a50040 RCX: 0000000000000001 > [ 33.468332] RDX: ffffea0001a50001 RSI: 0000000000000000 RDI: ffffea0001a50040 > [ 33.468332] RBP: ffff88006bdafc58 R08: 0000000000000000 R09: 0000000000000000 > [ 33.468332] R10: 0000000000000000 R11: 0000000000000001 R12: 00007f4983601000 > [ 33.468332] R13: 0000000000000001 R14: ffff88006bdafd70 R15: 0000000000000000 > [ 33.468332] FS: 00007f4983fa4700(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000 > [ 33.468332] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > [ 33.468332] CR2: 00007f4983601000 CR3: 000000007becb000 CR4: 00000000000006a0 > [ 33.468332] Stack: > [ 33.468332] ffff88006bf2ed00 00000000831169c0 ffffea0001a50040 00007f4983601000 > [ 33.468332] ffff88006bdafce8 ffff88006bdafd38 ffff88006bdafd70 ffff88007bf13a80 > [ 33.468332] ffff88006bdafcb0 ffffffff8113329a ffff88006bdafd80 0000000000000000 > [ 33.468332] Call Trace: > [ 33.468332] [<ffffffff8113329a>] futex_wait_setup+0x4a/0x1d0 > [ 33.468332] [<ffffffff81133540>] futex_wait+0x120/0x330 > [ 33.468332] [<ffffffff8111def0>] ? enqueue_hrtimer+0x50/0x50 > [ 33.468332] [<ffffffff8113587e>] do_futex+0x11e/0x1050 > [ 33.468332] [<ffffffff810e9825>] ? __lock_acquire+0x8c5/0x2830 > [ 33.468332] [<ffffffff8105da35>] ? kvm_clock_read+0x35/0x50 > [ 33.468332] [<ffffffff8105da91>] ? kvm_clock_get_cycles+0x11/0x20 > [ 33.468332] [<ffffffff81136860>] SyS_futex+0xb0/0x240 > [ 33.468332] [<ffffffff81cc3db2>] entry_SYSCALL_64_fastpath+0x12/0x76 > [ 33.468332] Code: 48 83 05 c9 e2 54 02 01 e9 56 ff ff ff 48 8b 57 20 f6 c2 01 0f 85 43 01 00 00 a8 01 0f 85 d2 00 00 00 41 83 4e 10 01 48 8b 47 08 <48> 8b 10 49 89 56 08 48 8b 07 f6 c4 40 0f 84 82 00 00 00 48 83 > [ 33.468332] RIP [<ffffffff81132b3a>] get_futex_key+0x2ba/0x410 > [ 33.468332] RSP <ffff88006bdafc18> > [ 33.483135] ---[ end trace 537578e223c13ed1 ]--- > [ 33.483502] Kernel panic - not syncing: Fatal exception > [ 33.484020] Kernel Offset: disabled > [ 33.484313] ---[ end Kernel panic - not syncing: Fatal exception > > This can be triggered with the following reproducer (based on > futex_wake04 test from ltp): > > #include <errno.h> > #include <stdio.h> > #include <stdint.h> > #include <unistd.h> > #include <linux/futex.h> > #include <sys/mman.h> > #include <sys/syscall.h> > #include <sys/time.h> > > #define HPGSZ 2097152 > int main(int argc, char **argv) { > long ret = 0; > void *addr; > uint32_t *futex; > int pgsz = getpagesize(); > > addr = mmap(NULL, HPGSZ, PROT_WRITE | PROT_READ, > MAP_SHARED | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0); > if (addr == MAP_FAILED) { > fprintf(stderr, "Failed to alloc hugepage\n"); > return -1; > } > > futex = (uint32_t *)((char *)addr + pgsz); > *futex = 0; > > ret = syscall(SYS_futex, futex, FUTEX_WAIT, *futex, NULL, NULL, 0); > if (ret < 0) { > perror("Syscall failed"); > } > > munmap(addr, HPGSZ); > > return 0; > } Thanks for report. Patch below fixes the issue for me. Could you test it as well? diff --git a/kernel/futex.c b/kernel/futex.c index 470c06c3299a..b29add22c454 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -470,6 +470,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) unsigned long address = (unsigned long)uaddr; struct mm_struct *mm = current->mm; struct page *page; + struct address_space *mapping; int err, ro = 0; /* @@ -535,7 +536,8 @@ again: * shmem_writepage move it from filecache to swapcache beneath us: * an unlikely race, but we do need to retry for page->mapping. */ - if (!page->mapping) { + mapping = compound_head(page)->mapping; + if (!mapping) { int shmem_swizzled = PageSwapCache(page); unlock_page(page); put_page(page); @@ -566,7 +568,7 @@ again: key->private.address = address; } else { key->both.offset |= FUT_OFF_INODE; /* inode-based key */ - key->shared.inode = page->mapping->host; + key->shared.inode = mapping->host; key->shared.pgoff = basepage_index(page); } -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>