* [PATCH] mm: Fix readahead_page_batch for retry entries
@ 2020-11-03 14:28 Matthew Wilcox (Oracle)
2020-11-04 1:10 ` Andrew Morton
0 siblings, 1 reply; 4+ messages in thread
From: Matthew Wilcox (Oracle) @ 2020-11-03 14:28 UTC (permalink / raw)
To: Andrew Morton, linux-fsdevel; +Cc: Matthew Wilcox, David Sterba, Wonhyuk Yang
Both btrfs and fuse have reported faults caused by seeing a retry
entry instead of the page they were looking for. This was caused
by a missing check in the iterator.
Reported-by: David Sterba <dsterba@suse.com>
Reported-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Fixes: 042124cc64c3 ("mm: add new readahead_control API")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index b921581a7dcf..2ea741c2bb16 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -751,6 +751,8 @@ static inline unsigned int __readahead_batch(struct readahead_control *rac,
xas_set(&xas, rac->_index);
rcu_read_lock();
xas_for_each(&xas, page, rac->_index + rac->_nr_pages - 1) {
+ if (xas_retry(&xas, page))
+ continue;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageTail(page), page);
array[i++] = page;
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: Fix readahead_page_batch for retry entries
2020-11-03 14:28 [PATCH] mm: Fix readahead_page_batch for retry entries Matthew Wilcox (Oracle)
@ 2020-11-04 1:10 ` Andrew Morton
2020-11-04 14:27 ` David Sterba
2020-11-05 2:33 ` Wonhyuk Yang
0 siblings, 2 replies; 4+ messages in thread
From: Andrew Morton @ 2020-11-04 1:10 UTC (permalink / raw)
To: Matthew Wilcox (Oracle); +Cc: linux-fsdevel, David Sterba, Wonhyuk Yang
On Tue, 3 Nov 2020 14:28:52 +0000 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:
> Both btrfs and fuse have reported faults caused by seeing a retry
> entry instead of the page they were looking for. This was caused
> by a missing check in the iterator.
Ambiguous. What sort of "faults"? Kernel pagefaults which cause
oopses?
It would be helpful to to provide sufficient info so that a reader of
this changelog can recognize whether this patch might fix some problem
which is being observed.
> Reported-by: David Sterba <dsterba@suse.com>
> Reported-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Perhaps via links to these reports.
> Fixes: 042124cc64c3 ("mm: add new readahead_control API")
So I'm assuming we need a cc:stable, but it isn't yet fully clear?
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
Please don't forget the "^---$" separator, thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: Fix readahead_page_batch for retry entries
2020-11-04 1:10 ` Andrew Morton
@ 2020-11-04 14:27 ` David Sterba
2020-11-05 2:33 ` Wonhyuk Yang
1 sibling, 0 replies; 4+ messages in thread
From: David Sterba @ 2020-11-04 14:27 UTC (permalink / raw)
To: Andrew Morton
Cc: Matthew Wilcox (Oracle), linux-fsdevel, David Sterba, Wonhyuk Yang
On Tue, Nov 03, 2020 at 05:10:54PM -0800, Andrew Morton wrote:
> On Tue, 3 Nov 2020 14:28:52 +0000 "Matthew Wilcox (Oracle)" <willy@infradead.org> wrote:
>
> > Both btrfs and fuse have reported faults caused by seeing a retry
> > entry instead of the page they were looking for. This was caused
> > by a missing check in the iterator.
>
> Ambiguous. What sort of "faults"? Kernel pagefaults which cause
> oopses?
>
> It would be helpful to to provide sufficient info so that a reader of
> this changelog can recognize whether this patch might fix some problem
> which is being observed.
>
> > Reported-by: David Sterba <dsterba@suse.com>
> > Reported-by: Wonhyuk Yang <vvghjk1234@gmail.com>
>
> Perhaps via links to these reports.
Reported by irc/mail, I'll try to dig the stack trace from the logs
again. The crash is hard to hit, there was just one occurence since 5.8
times.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm: Fix readahead_page_batch for retry entries
2020-11-04 1:10 ` Andrew Morton
2020-11-04 14:27 ` David Sterba
@ 2020-11-05 2:33 ` Wonhyuk Yang
1 sibling, 0 replies; 4+ messages in thread
From: Wonhyuk Yang @ 2020-11-05 2:33 UTC (permalink / raw)
To: Andrew Morton; +Cc: Matthew Wilcox (Oracle), linux-fsdevel, David Sterba
On Wed, Nov 4, 2020 at 10:10 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> It would be helpful to to provide sufficient info so that a reader of
> this changelog can recognize whether this patch might fix some problem
> which is being observed.
As you can see below the panic log, the accessing 0x402 causes panic.
In the xarray.h, 0x402 means RETRY_ENTRY.
BUG: kernel NULL pointer dereference, address: 0000000000000402
CPU: 14 PID: 306003 Comm: as Not tainted 5.9.0-1-amd64 #1 Debian 5.9.1-1
Hardware name: Lenovo ThinkSystem SR665/7D2VCTO1WW, BIOS D8E106Q-1.01 05/30/2020
RIP: 0010:fuse_readahead+0x152/0x470 [fuse]
Code: 41 8b 57 18 4c 8d 54 10 ff 4c 89 d6 48 8d 7c 24 10 e8 d2 e3 28
f9 48 85 c0 0f 84 fe 00 00 00 44 89 f2 49 89 04 d4 44 8d 72 01 <48> 8b
10 41 8b 4f 1c 48 c1 ea 10 83 e2 01 80 fa 01 19 d2 81 e2 01
RSP: 0018:ffffad99ceaebc50 EFLAGS: 00010246
RAX: 0000000000000402 RBX: 0000000000000001 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffff94c5af90bd98 RDI: ffffad99ceaebc60
RBP: ffff94ddc1749a00 R08: 0000000000000402 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000100 R12: ffff94de6c429ce0
R13: ffff94de6c4d3700 R14: 0000000000000001 R15: ffffad99ceaebd68
FS: 00007f228c5c7040(0000) GS:ffff94de8ed80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000402 CR3: 0000001dbd9b4000 CR4: 0000000000350ee0
Call Trace:
read_pages+0x83/0x270
page_cache_readahead_unbounded+0x197/0x230
generic_file_buffered_read+0x57a/0xa20
new_sync_read+0x112/0x1a0
vfs_read+0xf8/0x180
ksys_read+0x5f/0xe0
do_syscall_64+0x33/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xa9
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-11-03 14:28 [PATCH] mm: Fix readahead_page_batch for retry entries Matthew Wilcox (Oracle)
2020-11-04 1:10 ` Andrew Morton
2020-11-04 14:27 ` David Sterba
2020-11-05 2:33 ` Wonhyuk Yang
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