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scan: retry reading metadata on error

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If label_scan encounters bad vg metadata, invalidate
bcache data for the device and reread the mda_header
and metadata text back to back.  With concurrent commands
modifying large metadata, it's possible that the entire
metadata area can be rewritten in the time between a
command reading the mda_header and reading the metadata
text that the header points to.  Since the label_scan
is just assembling an initial overview of devices, it
doesn't use locking to serialize with other commands
that may be modifying the vg metadata at the same time.
This commit is contained in:
David Teigland 2021-06-28 18:10:47 -05:00
parent d89942d157
commit e035e32350
4 changed files with 49 additions and 0 deletions
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8
lib/format_text/format-text.c
View File

@ -1563,6 +1563,14 @@ int read_metadata_location_summary(const struct format_type *fmt,
return 0;
}
/*
* This code reading the start of the metadata area and verifying that
* it looks like a vgname can be removed. The checksum verifies it.
*/
log_debug_metadata("Reading metadata_vgname summary from %s at %llu",
dev_name(dev_area->dev),
(unsigned long long)(dev_area->start + rlocn->offset));
memset(namebuf, 0, sizeof(namebuf));
if (!dev_read_bytes(dev_area->dev, dev_area->start + rlocn->offset, NAME_LEN, namebuf))

35
lib/format_text/text_label.c
View File

@ -327,6 +327,9 @@ static int _read_mda_header_and_metadata(const struct format_type *fmt,
{
struct mda_context *mdac = (struct mda_context *) mda->metadata_locn;
struct mda_header *mdah;
int retries = 0;
retry:
if (!(mdah = raw_read_mda_header(fmt, &mdac->area, (mda->mda_num == 1), 0, bad_fields))) {
log_warn("WARNING: bad metadata header on %s at %llu.",
@ -354,6 +357,38 @@ static int _read_mda_header_and_metadata(const struct format_type *fmt,
if (vgsummary->zero_offset)
return 1;
/*
* This code is used by label_scan to get a summary of the
* VG metadata that will be properly read later by vg_read.
* The initial read of this device during label_scan
* populates bcache with the first 128K of data from the
* device. That block of data contains the mda_header
* (at 4k) but will often not include the metadata text,
* which is often located further into the metadata area
* (beyond the 128K block saved in bcache.)
* So read_metadata_location_summary will usually get the
* mda_header from bcache which was read initially, and
* then it will often need to do a new disk read to get
* the actual metadata text that the mda_header points to.
* Since there is no locking around label_scan, it's
* possible (but very rare) that the entire metadata area
* can be rewritten by other commands between the time that
* this command read the mda_header and the time that it
* reads the metadata text. This means the expected metadata
* text isn't found, and an error is returned here.
* To handle this, invalidate all data in bcache for this
* device and reread the mda_header and metadata text back to
* back, so inconsistency is less likely (without locking
* there's no guarantee, e.g. if the command is blocked
* somehow between the two reads.)
*/
if (!retries) {
log_print("Retrying metadata scan.");
retries++;
dev_invalidate(mdac->area.dev);
goto retry;
}
log_warn("WARNING: bad metadata text on %s in mda%d",
dev_name(mdac->area.dev), mda->mda_num);
*bad_fields |= BAD_MDA_TEXT;

5
lib/label/label.c
View File

@ -1704,6 +1704,11 @@ bool dev_invalidate_bytes(struct device *dev, uint64_t start, size_t len)
return bcache_invalidate_bytes(scan_bcache, dev->bcache_di, start, len);
}
void dev_invalidate(struct device *dev)
{
bcache_invalidate_di(scan_bcache, dev->bcache_di);
}
bool dev_write_zeros(struct device *dev, uint64_t start, size_t len)
{
return dev_set_bytes(dev, start, len, 0);

1
lib/label/label.h
View File

@ -130,6 +130,7 @@ bool dev_write_bytes(struct device *dev, uint64_t start, size_t len, void *data)
bool dev_write_zeros(struct device *dev, uint64_t start, size_t len);
bool dev_set_bytes(struct device *dev, uint64_t start, size_t len, uint8_t val);
bool dev_invalidate_bytes(struct device *dev, uint64_t start, size_t len);
void dev_invalidate(struct device *dev);
void dev_set_last_byte(struct device *dev, uint64_t offset);
void dev_unset_last_byte(struct device *dev);