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Matthew Wilcox (Oracle) 07378b0991 xarray: Fix early termination of xas_for_each_marked 
commit 7e934cf5ac upstream.

xas_for_each_marked() is using entry == NULL as a termination condition
of the iteration. When xas_for_each_marked() is used protected only by
RCU, this can however race with xas_store(xas, NULL) in the following
way:

TASK1                                   TASK2
page_cache_delete()         	        find_get_pages_range_tag()
                                          xas_for_each_marked()
                                            xas_find_marked()
                                              off = xas_find_chunk()

  xas_store(&xas, NULL)
    xas_init_marks(&xas);
    ...
    rcu_assign_pointer(*slot, NULL);
                                              entry = xa_entry(off);

And thus xas_for_each_marked() terminates prematurely possibly leading
to missed entries in the iteration (translating to missing writeback of
some pages or a similar problem).

If we find a NULL entry that has been marked, skip it (unless we're trying
to allocate an entry).

Reported-by: Jan Kara <jack@suse.cz>
CC: stable@vger.kernel.org
Fixes: ef8e5717db ("page cache: Convert delete_batch to XArray")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-04-17 10:50:18 +02:00
..
acpi ACPICA: Allow acpi_any_gpe_status_set() to skip one GPE 2020-04-17 10:50:09 +02:00
asm-generic lib/vdso: Make __arch_update_vdso_data() logic understandable 2020-03-05 16:43:49 +01:00
clocksource
crypto crypto: algif_skcipher - Use chunksize instead of blocksize 2020-01-17 19:48:46 +01:00
drm drm: mst: Fix query_payload ack reply struct 2019-12-31 16:42:19 +01:00
dt-bindings clk: imx8mn: Fix incorrect clock defines 2020-03-18 07:17:55 +01:00
keys
kvm
linux xarray: Fix early termination of xas_for_each_marked 2020-04-17 10:50:18 +02:00
math-emu
media media: rc: add keymap for Videostrong KII Pro 2020-04-17 10:49:59 +02:00
misc
net rxrpc: Fix call interruptibility handling 2020-04-17 10:49:57 +02:00
pcmcia
ras
rdma IB/core: Let IB core distribute cache update events 2020-02-24 08:36:26 +01:00
scsi scsi: Revert "target: iscsi: Wait for all commands to finish before freeing a session" 2020-02-28 17:22:25 +01:00
soc
sound ALSA: rawmidi: Avoid bit fields for state flags 2020-02-28 17:22:27 +01:00
target
trace afs: Fix some tracing details 2020-04-01 11:02:08 +02:00
uapi include/uapi/linux/swab.h: fix userspace breakage, use __BITS_PER_LONG for swap 2020-04-13 10:48:12 +02:00
vdso
video
xen xen: fixes and cleanups for 5.4-rc2 2019-10-04 11:13:09 -07:00