----- Original Message -----
On Tue, Dec 03, 2019 at 07:50:39AM -0500, Jan Stancek wrote:
My theory is that there's a race in iomap. There appear to be interleaved calls to iomap_set_range_uptodate() for same page with varying offset and length. Each call sees bitmap as _not_ entirely "uptodate" and hence doesn't call SetPageUptodate(). Even though each bit in bitmap ends up uptodate by the time all calls finish.
Weird. That should be prevented by the page lock that all callers of iomap_set_range_uptodate. But in case I miss something, does the patch below trigger? If not it is not jut a race, but might be some weird ordering problem with the bitops, especially if it only triggers on ppc, which is very weakly ordered.
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index d33c7bc5ee92..25e942c71590 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -148,6 +148,8 @@ iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len) unsigned int i; bool uptodate = true;
- WARN_ON_ONCE(!PageLocked(page));
- if (iop) { for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) { if (i >= first && i <= last)
Hit it pretty quick this time:
# uptime 09:27:42 up 22 min, 2 users, load average: 0.09, 13.38, 26.18
# /mnt/testarea/ltp/testcases/bin/genbessel Bus error (core dumped)
# dmesg | grep -i -e warn -e call [ 0.000000] dt-cpu-ftrs: not enabling: system-call-vectored (disabled or unsupported by kernel) [ 0.000000] random: get_random_u64 called from cache_random_seq_create+0x98/0x1e0 with crng_init=0 [ 0.000000] rcu: Offload RCU callbacks from CPUs: (none). [ 5.312075] megaraid_sas 0031:01:00.0: megasas_disable_intr_fusion is called outbound_intr_mask:0x40000009 [ 5.357307] megaraid_sas 0031:01:00.0: megasas_disable_intr_fusion is called outbound_intr_mask:0x40000009 [ 5.485126] megaraid_sas 0031:01:00.0: megasas_enable_intr_fusion is called outbound_intr_mask:0x40000000
So, extra WARN_ON_ONCE applied on top of v5.4-8836-g81b6b96475ac did not trigger.
Is it possible for iomap code to submit multiple bio-s for same locked page and then receive callbacks in parallel?