linux-toradex.git/drivers/md/dm-bufio.c, branch v3.4.96

dm bufio: avoid a possible __vmalloc deadlock

2014-06-07T23:02:05+00:00

commit 502624bdad3dba45dfaacaf36b7d83e39e74b2d2 upstream.

This patch uses memalloc_noio_save to avoid a possible deadlock in
dm-bufio.  (it could happen only with large block size, at most
PAGE_SIZE << MAX_ORDER (typically 8MiB).

__vmalloc doesn't fully respect gfp flags. The specified gfp flags are
used for allocation of requested pages, structures vmap_area, vmap_block
and vm_struct and the radix tree nodes.

However, the kernel pagetables are allocated always with GFP_KERNEL.
Thus the allocation of pagetables can recurse back to the I/O layer and
cause a deadlock.

This patch uses the function memalloc_noio_save to set per-process
PF_MEMALLOC_NOIO flag and the function memalloc_noio_restore to restore
it. When this flag is set, all allocations in the process are done with
implied GFP_NOIO flag, thus the deadlock can't happen.

This should be backported to stable kernels, but they don't have the
PF_MEMALLOC_NOIO flag and memalloc_noio_save/memalloc_noio_restore
functions. So, PF_MEMALLOC should be set and restored instead.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon 
[bwh: Backported to 3.2 as recommended]
Signed-off-by: Ben Hutchings 
Cc: Rui Xiang 
Signed-off-by: Greg Kroah-Hartman

dm bufio: initialize read-only module parameters

2013-12-20T15:34:20+00:00

commit 4cb57ab4a2e61978f3a9b7d4f53988f30d61c27f upstream.

Some module parameters in dm-bufio are read-only. These parameters
inform the user about memory consumption. They are not supposed to be
changed by the user.

However, despite being read-only, these parameters can be set on
modprobe or insmod command line, for example:
modprobe dm-bufio current_allocated_bytes=12345

The kernel doesn't expect that these variables can be non-zero at module
initialization and if the user sets them, it results in BUG.

This patch initializes the variables in the module init routine, so that
user-supplied values are ignored.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Mike Snitzer 
Signed-off-by: Greg Kroah-Hartman

dm bufio: prefetch

2012-03-28T17:41:29+00:00

This patch introduces a new function dm_bufio_prefetch. It prefetches
the specified range of blocks into dm-bufio cache without waiting
for i/o completion.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon

dm-bufio.c: there's no need to include linux/version.h

2012-02-03T21:38:12+00:00

As 'make versioncheck' points out, drivers/md/dm-bufio.c has no need to include
linux/version.h, so this patch removes the unneeded include.

Signed-off-by: Jesper Juhl 
Acked-by: Mikulas Patocka 
Signed-off-by: Jiri Kosina

device-mapper: dm-bufio.c needs to include module.h

2011-11-07T18:29:10+00:00

since it uses the module facilities.

Reported-by: Witold Baryluk 
Signed-off-by: Stephen Rothwell 
Signed-off-by: Paul Gortmaker 
Signed-off-by: Linus Torvalds

dm: add bufio

2011-10-31T20:19:09+00:00

The dm-bufio interface allows you to do cached I/O on devices,
holding recently-read blocks in memory and performing delayed writes.

We don't use buffer cache or page cache already present in the kernel, because:
* we need to handle block sizes larger than a page
* we can't allocate memory to perform reads or we'd have deadlocks

Currently, when a cache is required, we limit its size to a fraction of
available memory.  Usage can be viewed and changed in
/sys/module/dm_bufio/parameters/ .

The first user is thin provisioning, but more dm users are planned.

Signed-off-by: Mikulas Patocka 
Signed-off-by: Alasdair G Kergon