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* [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later
       [not found]     ` <1420623640.14527843.1575289859701.JavaMail.zimbra@redhat.com>
@ 2019-12-03 12:50       ` Jan Stancek
  2019-12-03 13:07         ` Christoph Hellwig
  2019-12-03 19:09         ` Christoph Hellwig
  0 siblings, 2 replies; 6+ messages in thread
From: Jan Stancek @ 2019-12-03 12:50 UTC (permalink / raw)
  To: linux-xfs, linux-fsdevel, hch, darrick.wong
  Cc: linuxppc-dev, Memory Management, LTP Mailing List,
	Linux Stable maillist, CKI Project, Michael Ellerman

Hi,

(This bug report is summary from thread [1] with some additions)

User-space binaries on Power9 ppc64le (with 64k pages) on xfs
filesystem are sporadically hitting SIGBUS:

---------- 8< ----------
(gdb) r
Starting program: /mnt/testarea/ltp/testcases/bin/genasin

Program received signal SIGBUS, Bus error.
dl_main (phdr=0x10000040, phnum=<optimized out>, user_entry=0x7fffffffe760, auxv=<optimized out>) at rtld.c:1362
1362        switch (ph->p_type)

(gdb) p ph
$1 = (const Elf64_Phdr *) 0x10000040

(gdb) p *ph
Cannot access memory at address 0x10000040

(gdb) info proc map
process 1110670
Mapped address spaces:

          Start Addr           End Addr       Size     Offset objfile
          0x10000000         0x10010000    0x10000        0x0 /mnt/testarea/ltp/testcases/bin/genasin
          0x10010000         0x10030000    0x20000        0x0 /mnt/testarea/ltp/testcases/bin/genasin
      0x7ffff7f90000     0x7ffff7fb0000    0x20000        0x0 [vdso]
      0x7ffff7fb0000     0x7ffff7fe0000    0x30000        0x0 /usr/lib64/ld-2.30.so
      0x7ffff7fe0000     0x7ffff8000000    0x20000    0x20000 /usr/lib64/ld-2.30.so
      0x7ffffffd0000     0x800000000000    0x30000        0x0 [stack]

(gdb) x/1x 0x10000040
0x10000040:     Cannot access memory at address 0x10000040
---------- >8 ----------

When this happens the binary continues to hit SIGBUS until page
is released, for example by: echo 3 > /proc/sys/vm/drop_caches

The issue goes back to at least v4.19.

I can semi-reliably reproduce it with LTP is installed to /mnt/testarea/ltp by:
while [ True ]; do
        echo 3 > /proc/sys/vm/drop_caches
        rm -f /mnt/testarea/ltp/results/RUNTEST.log /mnt/testarea/ltp/output/RUNTEST.run.log
        ./runltp -p -d results -l RUNTEST.log -o RUNTEST.run.log -f math
        grep FAIL /mnt/testarea/ltp/results/RUNTEST.log && exit 1
done

and some stress activity in other terminal (e.g. kernel build).
Sometimes in minutes, sometimes in hours. It is not reliable
enough to get meaningful bisect results.

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.

For example, with following traces:

iomap_set_range_uptodate()
...
        if (uptodate && !PageError(page))
                SetPageUptodate(page);
+       
+       if (mycheck(page)) {
+               trace_printk("page: %px, iop: %px, uptodate: %d, !PageError(page): %d, flags: %lx\n", page, iop, uptodate, !PageError(page), page->flags);
+               trace_printk("first: %u, last: %u, off: %u, len: %u, i: %u\n", first, last, off, len, i);
+       }

I get:
         genacos-18471 [057] ....   162.465730: iomap_readpages: mapping: c000003f185a1ab0
         genacos-18471 [057] ....   162.465732: iomap_page_create: iomap_page_create page: c00c00000fe26180, page->private: 0000000000000000, iop: c000003fc70a19c0, flags: 3ffff800000001
         genacos-18471 [057] ....   162.465736: iomap_set_range_uptodate: page: c00c00000fe26180, iop: c000003fc70a19c0, uptodate: 0, !PageError(page): 1, flags: 3ffff800002001
         genacos-18471 [057] ....   162.465736: iomap_set_range_uptodate: first: 1, last: 14, off: 4096, len: 57344, i: 16
          <idle>-0     [060] ..s.   162.534862: iomap_set_range_uptodate: page: c00c00000fe26180, iop: c000003fc70a19c0, uptodate: 0, !PageError(page): 1, flags: 3ffff800002081
          <idle>-0     [061] ..s.   162.534862: iomap_set_range_uptodate: page: c00c00000fe26180, iop: c000003fc70a19c0, uptodate: 0, !PageError(page): 1, flags: 3ffff800002081
          <idle>-0     [060] ..s.   162.534864: iomap_set_range_uptodate: first: 0, last: 0, off: 0, len: 4096, i: 16
          <idle>-0     [061] ..s.   162.534864: iomap_set_range_uptodate: first: 15, last: 15, off: 61440, len: 4096, i: 16

This page doesn't have Uptodate flag set, which leads to filemap_fault()
returning VM_FAULT_SIGBUS:

crash> p/x ((struct page *) 0xc00c00000fe26180)->flags                                                                                                                                             
$1 = 0x3ffff800002032

crash> kmem -g 0x3ffff800002032
FLAGS: 3ffff800002032
  PAGE-FLAG       BIT  VALUE
  PG_error          1  0000002
  PG_dirty          4  0000010
  PG_lru            5  0000020
  PG_private_2     13  0002000
  PG_fscache       13  0002000
  PG_savepinned     4  0000010
  PG_double_map    13  0002000

But iomap_page->uptodate in page->private suggests all bits are uptodate:

crash> p/x ((struct page *) 0xc00c00000fe26180)->private
$2 = 0xc000003fc70a19c0

crash> p/x ((struct iomap_page *) 0xc000003fc70a19c0)->uptodate                                                                                                                                    
$3 = {0xffff, 0x0}


It appears (after ~4 hours) that I can avoid the problem if I split
the loop so that bits are checked only after all updates are made.
Not sure if this correct approach, or just making it less reproducible:

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index e25901ae3ff4..abe37031c93d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -131,7 +131,11 @@ iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
                for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
                        if (i >= first && i <= last)
                                set_bit(i, iop->uptodate);
-                       else if (!test_bit(i, iop->uptodate))
+               }
+               for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
+                       if (i >= first && i <= last)
+                               continue;
+                       if (!test_bit(i, iop->uptodate))
                                uptodate = false;
                }
        }

Thanks,
Jan

[1] https://lore.kernel.org/stable/1420623640.14527843.1575289859701.JavaMail.zimbra@redhat.com/T/#u


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later
  2019-12-03 12:50       ` [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later Jan Stancek
@ 2019-12-03 13:07         ` Christoph Hellwig
  2019-12-03 14:35           ` Jan Stancek
  2019-12-03 19:09         ` Christoph Hellwig
  1 sibling, 1 reply; 6+ messages in thread
From: Christoph Hellwig @ 2019-12-03 13:07 UTC (permalink / raw)
  To: Jan Stancek
  Cc: linux-xfs, linux-fsdevel, hch, darrick.wong, linuxppc-dev,
	Memory Management, LTP Mailing List, Linux Stable maillist,
	CKI Project, Michael Ellerman

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)

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later
  2019-12-03 13:07         ` Christoph Hellwig
@ 2019-12-03 14:35           ` Jan Stancek
  2019-12-03 16:08             ` Darrick J. Wong
  0 siblings, 1 reply; 6+ messages in thread
From: Jan Stancek @ 2019-12-03 14:35 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: linux-xfs, linux-fsdevel, darrick wong, linuxppc-dev,
	Memory Management, LTP Mailing List, Linux Stable maillist,
	CKI Project, Michael Ellerman


----- 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?


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later
  2019-12-03 14:35           ` Jan Stancek
@ 2019-12-03 16:08             ` Darrick J. Wong
  0 siblings, 0 replies; 6+ messages in thread
From: Darrick J. Wong @ 2019-12-03 16:08 UTC (permalink / raw)
  To: Jan Stancek
  Cc: Christoph Hellwig, linux-xfs, linux-fsdevel, linuxppc-dev,
	Memory Management, LTP Mailing List, Linux Stable maillist,
	CKI Project, Michael Ellerman

On Tue, Dec 03, 2019 at 09:35:28AM -0500, Jan Stancek wrote:
> 
> ----- 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?

Yes, if (say) you have 64k pages on a 4k-block filesystem and the extent
mapping for all 16 blocks aren't contiguous, then iomap will issue
separate bios for each physical fragment it finds.  iomap will call
submit_bio on those bios whenever it thinks it's done filling the bio,
so you can indeed get multiple callbacks in parallel.

--D

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later
  2019-12-03 12:50       ` [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later Jan Stancek
  2019-12-03 13:07         ` Christoph Hellwig
@ 2019-12-03 19:09         ` Christoph Hellwig
  2019-12-04 14:43           ` Jan Stancek
  1 sibling, 1 reply; 6+ messages in thread
From: Christoph Hellwig @ 2019-12-03 19:09 UTC (permalink / raw)
  To: Jan Stancek
  Cc: linux-xfs, linux-fsdevel, hch, darrick.wong, linuxppc-dev,
	Memory Management, LTP Mailing List, Linux Stable maillist,
	CKI Project, Michael Ellerman

Please try the patch below:

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 512856a88106..340c15400423 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -28,6 +28,7 @@
 struct iomap_page {
 	atomic_t		read_count;
 	atomic_t		write_count;
+	spinlock_t		uptodate_lock;
 	DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
 };
 
@@ -51,6 +52,7 @@ iomap_page_create(struct inode *inode, struct page *page)
 	iop = kmalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);
 	atomic_set(&iop->read_count, 0);
 	atomic_set(&iop->write_count, 0);
+	spin_lock_init(&iop->uptodate_lock);
 	bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);
 
 	/*
@@ -139,25 +141,38 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
 }
 
 static void
-iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
+iomap_iop_set_range_uptodate(struct page *page, unsigned off, unsigned len)
 {
 	struct iomap_page *iop = to_iomap_page(page);
 	struct inode *inode = page->mapping->host;
 	unsigned first = off >> inode->i_blkbits;
 	unsigned last = (off + len - 1) >> inode->i_blkbits;
-	unsigned int i;
 	bool uptodate = true;
+	unsigned long flags;
+	unsigned int i;
 
-	if (iop) {
-		for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
-			if (i >= first && i <= last)
-				set_bit(i, iop->uptodate);
-			else if (!test_bit(i, iop->uptodate))
-				uptodate = false;
-		}
+	spin_lock_irqsave(&iop->uptodate_lock, flags);
+	for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
+		if (i >= first && i <= last)
+			set_bit(i, iop->uptodate);
+		else if (!test_bit(i, iop->uptodate))
+			uptodate = false;
 	}
 
-	if (uptodate && !PageError(page))
+	if (uptodate)
+		SetPageUptodate(page);
+	spin_unlock_irqrestore(&iop->uptodate_lock, flags);
+}
+
+static void
+iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
+{
+	if (PageError(page))
+		return;
+
+	if (page_has_private(page))
+		iomap_iop_set_range_uptodate(page, off, len);
+	else
 		SetPageUptodate(page);
 }
 

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later
  2019-12-03 19:09         ` Christoph Hellwig
@ 2019-12-04 14:43           ` Jan Stancek
  0 siblings, 0 replies; 6+ messages in thread
From: Jan Stancek @ 2019-12-04 14:43 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: linux-xfs, linux-fsdevel, darrick wong, linuxppc-dev,
	Memory Management, LTP Mailing List, Linux Stable maillist,
	CKI Project, Michael Ellerman


----- Original Message -----
> Please try the patch below:

I ran reproducer for 18 hours on 2 systems were it previously reproduced,
there were no crashes / SIGBUS.


^ permalink raw reply	[flat|nested] 6+ messages in thread

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Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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     [not found]     ` <1420623640.14527843.1575289859701.JavaMail.zimbra@redhat.com>
2019-12-03 12:50       ` [bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later Jan Stancek
2019-12-03 13:07         ` Christoph Hellwig
2019-12-03 14:35           ` Jan Stancek
2019-12-03 16:08             ` Darrick J. Wong
2019-12-03 19:09         ` Christoph Hellwig
2019-12-04 14:43           ` Jan Stancek

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