Hi Ritesh, On 02.06.2020 15:47, Ritesh Harjani wrote: > It doesn't really matter in ext4_mb_new_blocks() about whether the code > is rescheduled on any other cpu due to preemption. Because we care > about discard_pa_seq only when the block allocation fails and then too > we add the seq counter of all the cpus against the initial sampled one > to check if anyone has freed any blocks while we were doing allocation. > > So just use raw_cpu_ptr instead of this_cpu_ptr to avoid this BUG. > > BUG: using smp_processor_id() in preemptible [00000000] code: syz-fuzzer/6927 > caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711 > CPU: 1 PID: 6927 Comm: syz-fuzzer Not tainted 5.7.0-next-20200602-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x18f/0x20d lib/dump_stack.c:118 > check_preemption_disabled+0x20d/0x220 lib/smp_processor_id.c:48 > ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711 > ext4_ext_map_blocks+0x201b/0x33e0 fs/ext4/extents.c:4244 > ext4_map_blocks+0x4cb/0x1640 fs/ext4/inode.c:626 > ext4_getblk+0xad/0x520 fs/ext4/inode.c:833 > ext4_bread+0x7c/0x380 fs/ext4/inode.c:883 > ext4_append+0x153/0x360 fs/ext4/namei.c:67 > ext4_init_new_dir fs/ext4/namei.c:2757 [inline] > ext4_mkdir+0x5e0/0xdf0 fs/ext4/namei.c:2802 > vfs_mkdir+0x419/0x690 fs/namei.c:3632 > do_mkdirat+0x21e/0x280 fs/namei.c:3655 > do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > Signed-off-by: Ritesh Harjani <[email protected]> > Reported-by: [email protected]
This fixes the warning observed on various Samsung Exynos SoC based boards with linux-next 20200602. Tested-by: Marek Szyprowski <[email protected]> > --- > fs/ext4/mballoc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index a9083113a8c0..b79b32dbe3ea 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -4708,7 +4708,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle, > } > > ac->ac_op = EXT4_MB_HISTORY_PREALLOC; > - seq = *this_cpu_ptr(&discard_pa_seq); > + seq = *raw_cpu_ptr(&discard_pa_seq); > if (!ext4_mb_use_preallocated(ac)) { > ac->ac_op = EXT4_MB_HISTORY_ALLOC; > ext4_mb_normalize_request(ac, ar); Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
