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Subject[PATCH 3.16 076/233] ext4: handle the rest of ext4_mb_load_buddy() ENOMEM errors
3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

commit 9651e6b2e20648d04d5e1fe6479a3056047e8781 upstream.

I've got another report about breaking ext4 by ENOMEM error returned from
ext4_mb_load_buddy() caused by memory shortage in memory cgroup.
This time inside ext4_discard_preallocations().

This patch replaces ext4_error() with ext4_warning() where errors returned
from ext4_mb_load_buddy() are not fatal and handled by caller:
* ext4_mb_discard_group_preallocations() - called before generating ENOSPC,
we'll try to discard other group or return ENOSPC into user-space.
* ext4_trim_all_free() - just stop trimming and return ENOMEM from ioctl.

Some callers cannot handle errors, thus __GFP_NOFAIL is used for them:
* ext4_discard_preallocations()
* ext4_mb_discard_lg_preallocations()

Fixes: adb7ef600cc9 ("ext4: use __GFP_NOFAIL in ext4_free_blocks()")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/mballoc.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3849,7 +3849,8 @@ ext4_mb_discard_group_preallocations(str

err = ext4_mb_load_buddy(sb, group, &e4b);
if (err) {
- ext4_error(sb, "Error loading buddy information for %u", group);
+ ext4_warning(sb, "Error %d loading buddy information for %u",
+ err, group);
put_bh(bitmap_bh);
return 0;
}
@@ -4006,10 +4007,11 @@ repeat:
BUG_ON(pa->pa_type != MB_INODE_PA);
group = ext4_get_group_number(sb, pa->pa_pstart);

- err = ext4_mb_load_buddy(sb, group, &e4b);
+ err = ext4_mb_load_buddy_gfp(sb, group, &e4b,
+ GFP_NOFS|__GFP_NOFAIL);
if (err) {
- ext4_error(sb, "Error loading buddy information for %u",
- group);
+ ext4_error(sb, "Error %d loading buddy information for %u",
+ err, group);
continue;
}

@@ -4264,11 +4266,14 @@ ext4_mb_discard_lg_preallocations(struct
spin_unlock(&lg->lg_prealloc_lock);

list_for_each_entry_safe(pa, tmp, &discard_list, u.pa_tmp_list) {
+ int err;

group = ext4_get_group_number(sb, pa->pa_pstart);
- if (ext4_mb_load_buddy(sb, group, &e4b)) {
- ext4_error(sb, "Error loading buddy information for %u",
- group);
+ err = ext4_mb_load_buddy_gfp(sb, group, &e4b,
+ GFP_NOFS|__GFP_NOFAIL);
+ if (err) {
+ ext4_error(sb, "Error %d loading buddy information for %u",
+ err, group);
continue;
}
ext4_lock_group(sb, group);
@@ -5107,8 +5112,8 @@ ext4_trim_all_free(struct super_block *s

ret = ext4_mb_load_buddy(sb, group, &e4b);
if (ret) {
- ext4_error(sb, "Error in loading buddy "
- "information for %u", group);
+ ext4_warning(sb, "Error %d loading buddy information for %u",
+ ret, group);
return ret;
}
bitmap = e4b.bd_bitmap;
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