The patch titled Subject: lib/buildid: use __kernel_read() for sleepable context has been added to the -mm mm-nonmm-unstable branch. Its filename is lib-buildid-use-__kernel_read-for-sleepable-context.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Shakeel Butt shakeel.butt@linux.dev Subject: lib/buildid: use __kernel_read() for sleepable context Date: Thu, 18 Dec 2025 12:55:05 -0800

For the sleepable context, convert freader to use __kernel_read() instead of direct page cache access via read_cache_folio(). This simplifies the faultable code path by using the standard kernel file reading interface which handles all the complexity of reading file data.

At the moment we are not changing the code for non-sleepable context which uses filemap_get_folio() and only succeeds if the target folios are already in memory and up-to-date. The reason is to keep the patch simple and easier to backport to stable kernels.

Syzbot repro does not crash the kernel anymore and the selftests run successfully.

In the follow up we will make __kernel_read() with IOCB_NOWAIT work for non-sleepable contexts. In addition, I would like to replace the secretmem check with a more generic approach and will add fstest for the buildid code.

Link: https://lkml.kernel.org/r/20251218205505.2415840-1-shakeel.butt@linux.dev Fixes: ad41251c290d ("lib/buildid: implement sleepable build_id_parse() API") Signed-off-by: Shakeel Butt shakeel.butt@linux.devReported-by: syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=09b7d050e4806540153d Reviewed-by: Christoph Hellwig hch@lst.de Cc: Alexei Starovoitov ast@kernel.org Cc: Andrii Nakryiko andrii@kernel.org Cc: Daniel Borkman daniel@iogearbox.net Cc: "Darrick J. Wong" djwong@kernel.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

lib/buildid.c | 47 +++++++++++++++++++++++++++++++++++------------ 1 file changed, 35 insertions(+), 12 deletions(-)

--- a/lib/buildid.c~lib-buildid-use-__kernel_read-for-sleepable-context +++ a/lib/buildid.c @@ -5,6 +5,7 @@ #include <linux/elf.h> #include <linux/kernel.h> #include <linux/pagemap.h> +#include <linux/fs.h> #include <linux/secretmem.h>

#define BUILD_ID 3 @@ -37,6 +38,29 @@ static void freader_put_folio(struct fre r->folio = NULL; }

+/* + * Data is read directly into r->buf. Returns pointer to the buffer + * on success, NULL on failure with r->err set. + */ +static const void *freader_fetch_sync(struct freader *r, loff_t file_off, size_t sz) +{ + ssize_t ret; + loff_t pos = file_off; + char *buf = r->buf; + + do { + ret = __kernel_read(r->file, buf, sz, &pos); + if (ret <= 0) { + r->err = ret ?: -EIO; + return NULL; + } + buf += ret; + sz -= ret; + } while (sz > 0); + + return r->buf; +} + static int freader_get_folio(struct freader *r, loff_t file_off) { /* check if we can just reuse current folio */ @@ -46,20 +70,9 @@ static int freader_get_folio(struct frea

freader_put_folio(r);

- /* reject secretmem folios created with memfd_secret() */ - if (secretmem_mapping(r->file->f_mapping)) - return -EFAULT; - + /* only use page cache lookup - fail if not already cached */ r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);

- /* if sleeping is allowed, wait for the page, if necessary */ - if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) { - filemap_invalidate_lock_shared(r->file->f_mapping); - r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT, - NULL, r->file); - filemap_invalidate_unlock_shared(r->file->f_mapping); - } - if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) { if (!IS_ERR(r->folio)) folio_put(r->folio); @@ -97,6 +110,16 @@ const void *freader_fetch(struct freader return r->data + file_off; }

+ /* reject secretmem folios created with memfd_secret() */ + if (secretmem_mapping(r->file->f_mapping)) { + r->err = -EFAULT; + return NULL; + } + + /* use __kernel_read() for sleepable context */ + if (r->may_fault) + return freader_fetch_sync(r, file_off, sz); + /* fetch or reuse folio for given file offset */ r->err = freader_get_folio(r, file_off); if (r->err) _

Patches currently in -mm which might be from shakeel.butt@linux.dev are

mm-memcg-fix-unit-conversion-for-k-macro-in-oom-log.patch lib-buildid-use-__kernel_read-for-sleepable-context.patch