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xfs: don't commit sunit/swidth updates to disk if that would cause repair failures

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Alex Lyakas reported[1] that mounting an xfs filesystem with new sunit
and swidth values could cause xfs_repair to fail loudly.  The problem
here is that repair calculates the where mkfs should have allocated the
root inode, based on the superblock geometry.  The allocation decisions
depend on sunit, which means that we really can't go updating sunit if
it would lead to a subsequent repair failure on an otherwise correct
filesystem.

Port from xfs_repair some code that computes the location of the root
inode and teach mount to skip the ondisk update if it would cause
problems for repair.  Along the way we'll update the documentation,
provide a function for computing the minimum AGFL size instead of
open-coding it, and cut down some indenting in the mount code.

Note that we allow the mount to proceed (and new allocations will
reflect this new geometry) because we've never screened this kind of
thing before.  We'll have to wait for a new future incompat feature to
enforce correct behavior, alas.

Note that the geometry reporting always uses the superblock values, not
the incore ones, so that is what xfs_info and xfs_growfs will report.

[1] https://lore.kernel.org/linux-xfs/20191125130744.GA44777@bfoster/T/#m00f9594b511e076e2fcdd489d78bc30216d72a7d

Reported-by: Alex Lyakas <alex@zadara.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
This commit is contained in:
Darrick J. Wong
2019-12-11 13:19:06 -08:00
parent 4f5b1b3a8f
commit 13eaec4b2a
4 changed files with 130 additions and 1 deletions
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45
fs/xfs/xfs_mount.c
View File

@@ -31,7 +31,7 @@
#include "xfs_reflink.h"
#include "xfs_extent_busy.h"
#include "xfs_health.h"
#include "xfs_trace.h"
static DEFINE_MUTEX(xfs_uuid_table_mutex);
static int xfs_uuid_table_size;
@@ -359,6 +359,42 @@ release_buf:
return error;
}
/*
* If the sunit/swidth change would move the precomputed root inode value, we
* must reject the ondisk change because repair will stumble over that.
* However, we allow the mount to proceed because we never rejected this
* combination before. Returns true to update the sb, false otherwise.
*/
static inline int
xfs_check_new_dalign(
struct xfs_mount *mp,
int new_dalign,
bool *update_sb)
{
struct xfs_sb *sbp = &mp->m_sb;
xfs_ino_t calc_ino;
calc_ino = xfs_ialloc_calc_rootino(mp, new_dalign);
trace_xfs_check_new_dalign(mp, new_dalign, calc_ino);
if (sbp->sb_rootino == calc_ino) {
*update_sb = true;
return 0;
}
xfs_warn(mp,
"Cannot change stripe alignment; would require moving root inode.");
/*
* XXX: Next time we add a new incompat feature, this should start
* returning -EINVAL to fail the mount. Until then, spit out a warning
* that we're ignoring the administrator's instructions.
*/
xfs_warn(mp, "Skipping superblock stripe alignment update.");
*update_sb = false;
return 0;
}
/*
* If we were provided with new sunit/swidth values as mount options, make sure
* that they pass basic alignment and superblock feature checks, and convert
@@ -419,10 +455,17 @@ xfs_update_alignment(
struct xfs_sb *sbp = &mp->m_sb;
if (mp->m_dalign) {
bool update_sb;
int error;
if (sbp->sb_unit == mp->m_dalign &&
sbp->sb_width == mp->m_swidth)
return 0;
error = xfs_check_new_dalign(mp, mp->m_dalign, &update_sb);
if (error || !update_sb)
return error;
sbp->sb_unit = mp->m_dalign;
sbp->sb_width = mp->m_swidth;
mp->m_update_sb = true;